I think elder millennials are definitely at the cutoff point for it. I'm in my early 30s so I'm a millenial with a capital M. Right in the middle of the generation. I'd also argue that we were the pivoting point for mainstream gaming.
Based on interactions with people my age and older I'd say the cutoff is closer to like 35 maybe 38? Even in my generation I remember growing up in high school and middle school that it wasnt as socially acceptable to play videogames for girls. As a 34 year old I'll say they werent uncommon and I played games with girls growing up and it wasnt hard to find girls my age in hs and college who played games, but it seems like the majority of girls were encouraged to age out of it. If I were to make up a number I'd say maybe 1/4 played video games? maybe half depending on the setting.
Even among guys I'd argue that after a certain age a majority of guys kept to a very specific type of game like sports games and maybe an FPS like halo or Cod.
It was during my late teens and early 20s that geek chic really took hold and it became more and more socially acceptable to like hobbies that were previously seen as childish or nerdy and it not be a big deal. I feel like a lot of "closeted" nerds and gamers became more open about the silly things they liked, and those who stopped because they were embarrassed as teens were willing to pick up a controller again.
The cultural shift happened right in the thick of things though so the closer you are to gen X the more likely you were expected to outgrow things and the closer you were to gen z the more you're allowed to just have fun.