I'm in my mid-30's, and four years ago I started going to as many meetups that seemed remotely interesting to me in a bunch of different groups, met a ton of acquaintances, and eventually quite a few friendships (that are hard to maintain for me, but I do make an effort).

I'm fairly introverted but I think the secret to why going to a bunch of meetups worked for me is I just kept showing up and did some small talk that people eventually got to know me and became friendlier and started inviting me to things due to familiarity.

In fact my closest friends right now I made by taken a chance at a random invite to a weekly game night by someone I met once at a meetup, and just kept showing up to his weekly events, and over time I became friends with everyone there.