An underrated benefit for grown-ass adults in age-agnostic spaces which happen to contain some teenagers is that you will be exposed to the things colloqually known as "what the kids these days are into". Now, the serious point is that this is good for resisting the urge to calcify– you have probably met at least one person who seems to have decided that learning about new stuff is too much work so they proudly refuse to bother. Don't be them!
The much funnier benefit is this is a good way learn things with which to unexpectedly conk a fellow grown-ass adult friend upside the head. Someone used to their kid cousin excitedly chattering about [topic they associate with kids] may not be expecting a fellow adult to bring it up out of nowhere, and this is consistently one of the funniest pranks I get to pull on my friends.