I’m in my 30’s and I’ve gotten into clans within the past couple of years or so. I started playing games that none of the rest of my friends played, like Hell Let Loose and Squad. Joining a clan for those two games was huge because it gave me a ton of people to play with at pretty much any time of day. For these types of games, at least, clans are still a pretty big thing. All of the clans that I’ve seen use Discord these days.
My Hell Let Loose clan has over 1,000 members and my Squad clan has even more - not entirely sure how many. What’s really interesting is that I know and have played with a ton of those members. Made lots of good memories, too.
Anyway, in my experience clans are totally still a thing. You should seek some out! Maybe you’ll find a good group that you vibe with.