I know about Magic The Gathering because of my younger son. I'm not sure when he started playing it, but I found out towards the end of his college stint, after he was married. It might have even been after his wife was expecting their first child.
He and a few work friends would play it, mostly on Saturdays.
Then, I was in a local comic book shop (can't remember what day it was, but it was in the afternoon) and there were a couple dozen people occupying an entire room (instead of comic books—those were confined to another room).
While I am into fantasy, and actually played Dungeons and Dragons once, I've never really been into role playing games. And to be honest, it was kind of disturbing to see so many 30-somethings and up playing. I felt like I was intruding!
Anyway, my son has been trying to get me to play with him—even offered to give me one of his decks. So far I've declined. I used to play video games with him and his brother (Halo mostly) but since they're both married and have been out of our house, we haven't played much of that together either. They've since moved on to Overwatch.