I don't think there is a cutoff.
My 80yo grandfather still pulls out the gamecube to play Mario Kart (and for a long time noone else could beat him). My grandmother before she passed was not really big on video games but would play one specific level of crash bandicoot over and over again.
My 45~yo mother streams minecraft in her free time and is even looking to start up a YouTube channel with more content. Some of her viewers are close to her age and when she was playing more Counter Strike than Minecraft the server she played on had adults of all ages on it.
I'm getting closer to 30 every year and I can't see myself ever quitting games. If/when I marry I imagine playing games will just be part of family bonding. I may get worse as I age like my grandfather but I doubt I'll ever stop.