Here, I'll start. When I was 8 years old, my parents went to a dinner party and plonked me down in front of the host's computer so I'd stay out of their way. The game they booted up to keep me occupied was Space Quest II. Little did they know what impact that would have on me...
I'm not entirely sure my first game counts as adventure, maybe more as a platform adventure, but for me it was back in probably around 1996 or 1997. I didn't have a computer at home, and during lunch break at school I joined the computer club. We had only two or three computers there that could have graphics and one of the games we could play was Prince of Persia. The second game I played there was Indiana Jones and the Fate of Atlantis.
I wouldn't say PoP is an adventure game, it's just a platformer with a simple story (like super mario) though Fate of Atlantis is an amazing first game to pop your adventure game cherry to
Fate of Atlantis was quite nice and challenging, especially when I could only play less then two or three hours a week. I've only finished this game years later.
Sorry for going off-topic since I know this isn't the main subject of this post, but I've been playing quite a few adventure games since I got a steamdeck, being bedridden this has really changed my life. TheBlackwell series and other wadjet eye games being some of my favourites. Currently I'm playing Broken Sword: Shadow of the Templars. I've played a lot of games I couldn't play when I was younger like I Have No Mouth and I Must Scream or Beneath a Steel Sky to name a few.
I'm a dad of young kids and the SteamDeck has basically re-enabled gaming for me, and is actually getting me to pay attention to my embarrassingly large backlog.
Played Return to Monkey Island on it when that came out.