I told this story a few times before, but it’s been a while, so here it is again. 
TL;DR: I started collecting when Pokémon was first released in The Netherlands mid-1999 when I was 7 years old, and casually collected until about 14/15 years old. Then I came back collecting mid-2015, and have been collecting since. (A short summary of my collection goals and what I own can be found near the bottom of this post.)
As for the whole story in detail:
When I was 7 years old me and my little brother were zapping on TV a bit when we came across a cartoon about a young boy throwing a red-white ball at a caterpillar (the end of episode 2). Intrigued, we continued watching the next episodes, and I’ve been hooked ever since. The next week our parents bought us our very first booster pack (English unlimited edition Base Set). I pulled a holo Chansey, and my little brother a holo Alakazam. As a kid I didn’t really care about holos though, unlike some classmates, so when someone offered me a Pidgey, Pidgeotto, AND Vulpix for my Chansey I gladly accepted. The more cards the better. That same week on the 8 o’clock news the Pokémon craze were the talk of the day. They stated some collectors even paid 100 Gulden (old Dutch currency) for some cards, and they showed a Charizard, and, you guessed it… a Chansey. Looking back they probably meant a 1st edition Shadowless version, but as a 7-year old kid I didn’t knew these differences existed, and I doubt the news reporter did either.
My second two packs were unlimited edition Jungle, which contained a holo Jolteon and holo Snorlax. I still have the Jolteon today (in Played condition 
), and it’s my favorite card from the Jungle set. The Snorlax I traded for a WB Mewtwo promo. The trade wasn’t too bad at the time, but now it would be a very, very bad trade.
Some other memorable pulls were a Shining Magikarp from Neo Revelations and Crystal Kingdra from Aquapolis (my brother had the Shining Gyarados and Crystal Nidoking. Quite funny how we remained even with our pulls, although he had a triple-star Shining Steelix I’ve been jealous of for quite a while. 
)
I’ve been collecting on and off until about the age of 14 or 15. I only opened a few booster packs a year, and never opened a booster box in my life at that time.
At the age of 18-20 I played Yu-Gi-Oh quite a lot online, and also bought cards to recreate those decks irl, even though I had no one to play with except for my little brother. Eventually I came across TrollAndToad.com where they not only sold Yu-Gi-Oh cards, but also Pokémon. I bought a Hitmonlee, Venusaur and Nidoking (the only three cards I was missing of the first 151 Pokémon).
Then, in August/September 2015 I came across all the Pikachus on TrollAndToad and bought all below 10 USD on impulse, which was basically the start of my Pikachu collection. At the time, my most expensive purchase was a Secret Rare Black Rose Dragon for 22 USD (oh, how times have changed! 
).
When the Pikachus arrived I had around 50, and I started looking online at how many existed at websites like Bulbapedia and forums. I bought all cheap ones I could find, but eventually started buying more expensive cards from TrollAndToad.com as well (< 50 USD). And it wasn’t long after, that I decided to also collect foreign Pikachu cards.
When searching for information online, I eventually came across justinator’s website. At the time, in December 2015, he had around 550 of the ~650 Pikachus, and only then I realized how many Pikachus actually existed. He owned or was searching for Pikachus I had never even seen before, and he was a real inspiration for me. When I joined the forum on February 21st, 2016 I had around 250 Pikachus, and my very first post was in Justin’s collection thread.
Then in August 2016 I created my own collection thread. At that point I had 472 Pikachus + 53 more incoming. Most of my story can then be found in that collection thread, but here are some highlights:
- In August 2016 my 500th Pikachu arrived: the English 5/5 Kids WB Creator Contest Pikachu.
- In September 2016 my very first Art Academy Pikachu had arrived. I paid more for it than any other card thus far (300 USD), so I wasn’t buying cards for less than 20 USD anymore by a long shot.
- In Augustus 2016 I started collecting Jumbo Pikachus as well, and one month later in October 2016 I already finished it. Apparently I choose the perfect time to collect them, and all except for two could be found on eBay.com right away. For one of the other two I use Noppin as middleman service for Yahoo Japan, which was the first time I had used YJ or a middleman service.
- In October 2016 I wrote my Base Pikachu artwork variations article, which has been expanded quite a lot over the years (although I still need to update it with the Celebrations cards and 25th anniversary Jumbos).
- In December 2016 my first Extended Artwork Base Pikachu arrived from Lunumbra (right now I have over 83 of them, from 83 different artists).
- In January 2017 I created my Instagram as well as my first Pikachu collection video. I had about 700 at the time, and had just surpassed Justin. A.f.a.i.k. I owned the largest Pikachu TCG collection in the world at the time. I also collected Sevipers since a few months prior (my favorite Pokémon), and after seeing the first few episode of Sun & Moon I decided to collect Mimikyus as well.
- In June 2017 the Matchprint Pikachu arrived which I bought from Rusty. The rarest Pikachu card I own (I paid 1k USD), with only two copies in existence.
- In August 2017 I made my 1st edition stamps variations article.
- In September 2017 I decided to collect the #21 Moltres promo in all raw and sealed variations, including the four English/japanese ones in PSA-10.
- In March 2018 my 1000th Pikachu arrived. Nothing too special: a Japanese 207/SM-P Pikachu, but defintely special for me.
- In June 2018 I started collecting Full Art Supporter cards, which was completed except for one card in July 2018.
- In December 2018 I bought that last card as well, the PSA-10 085/SM-P The Masked Royal, which apart from my first car was my most expensive purchase ever (I’ve bought it for 3.4k USD)
- In February 2019 when the Team Up set was released I decided to stop collecting Mimikyu, since that set contained 10 FA Supporters; 4 Pikachu; and 6 Mimikyu, multiplied by (at the time) 10 active languages.
- In May 2019 I collected and posted my National Index collecting including all Forms & Shiny Pokémon.
- In June 2019, after it was lost in Paris for three months, my pop-1 BGS Black Label Moltres arrived.
- In September 2019 I took over my little brother’s childhood collection.
- In September-November 2019 I was collecting one of each Yu-Gi-Oh rarity, and also made an article for it
- In October 2020 I completed my Seviper collecting by adding the Japanese unlimited WCP Seviper, the last card I was missing. A.f.a.i.k. I owned the first and only completed single Pokémon collection in all available languages/variations at the time (although I know of three such collections now)
- In November 2020 I started my ‘Pikachu around the World’ collection series, starting with the first alphabetical language Chinese. In this series I went over my ENTIRE Pikachu collection, one language/category at a time.
- In December 2020 my 1500th unique Pikachu card arrived, the French Pikachu Vmax Hyper Rare
- From February 27th, 2021 (25th Pokémon Day) onward I decided to only collect all English Pikachu, and one of each Japanese-exclusive artwork, for new releases, since it was too expensive to continue with all languages. The only exception are the Base Set artwork variations, for which I still get all languages.
- In May 2021 my most expensive bought card thus far arrived, the German Birthday Pikachu, for which I paid 3.6k euros (~4.4k USD at the time)
- In September 2021 I started and completed my XY BREAKthrough 124/162 Swablu collection, my second favorite TCG artwork after the Moltres #21 WotC promo
- In October 2021 I completed my Ancient Mew PSA-10 sixtet, as well as another small (14-card) collection: the first card released in each TCG language
- In April 2022 I completed writing my ‘Pikachu around the World’ collection series. The last part, with links to all the previous parts at the top, can be found here.
- In May 2022 I started my ‘Non-TCG Seviper’ collection series, with the first part: plushies and figures.
As for a summary of my current collections and their states:
- Pikachu: I own 1712 unique Pikachu TCG cards; with 6 more incoming; and 84 additional altered/extended cards. I’m currently missing just 10 (out of 1433) Pikachu cards released prior to February 27th, 2021 to ‘complete’ my collection goal.
- Seviper: My Seviper collection is 100% complete in all languages and variations.
- Full Art Supporters and Character Rares: 100% complete, except for some incoming cards from the latest sets, and I’m still waiting for some Japanese cards to release in English
- Moltres WotC #21 promo artwork: Only missing the sealed Swedish variation to complete it (and preferably also a GRAAD-9+ Italian Moltres). A CGC Perfect quad-10 is currently incoming.
- Ancient Mew PSA-10 sixtet: Completed.
- Swablu BREAKthrough 124/162 artwork: 100% completed.
- First card released in each (of the 14) TCG languages: 100% completed.
-
Seviper non-TCG: Ongoing. Currently missing five figures; and quite a few stickers and non-TCG cards and such. But I do have a lot of products/items already, which I’ll show in my collection thread over time.
National Index Collection including forms / Shiny Pokémon:
Yu-Gi-Oh rarity collection:
Mimikyu collection:
All three of these I’ve stopped, and probably won’t pick up anymore. Mimikyu I’ve stopped soon after the Team Up set was released in February 2019; the National Index collection I had completed up to the Sun & Moon era, and stopped just before the Sword & Shield era started at the start of 2020; the Yu-Gi-Oh rarity collection was complete except for one rarity exclusively used on Trophy cards, and some misprinted rarities, but I’ve stopped it around mid-2020. I might continue this last collection eventually, if only the English and Korean Ten Thousand Dragon wasn’t so expensive… 
In general: I currently own 13,263 unique non-duplicated Pokémon TCG cards; one sealed booster box; four sealed Decks; and eight sealed booster packs, with roughly 10k more duplicated cards I have yet to sell…
All in all it’s been a great journey so far, and sharing things like this with this awesome community is a great part of my collecting experience as well. Here’s to many more amazing Pokémon related years!! 
Greetz,
Quuador