When I was 15 I was playing 8 hours on weekdays, 19 hours on weekends. (Around 78 hours a week) I was in a guild. I attended meetings, I was on call, I worked my butt off and become the best player in my guild and was known by name in the server. I would use mathematics to get an edge seeking out every stat every angle. I ate, slept, and did my homework at that computer desk. It was my life.
I'm 25 now, I graduated college, I work full time, and I'm married. I now spend 2 hours gaming on weekdays and 5 hours on weekends. (20 hours a week). I am no longer in a serious guild and anyone who calls me after 9pm has a death wish. In fact I wouldn't have even 20 hours if I hadn't married a gamer girl. So yes I would say I have "grown out" of gaming. I no longer can afford to allow myself to be so submerged into that fantasy land. I have responsibilities, people who rely on me, money to be made. I suspect that as I get older my gaming time will be even less.
It is more because of the tragedy of become an adult though more than age. I never really got into Counter Strike or any of those FPS multiplayers. So the fact that my reaction time isn't as good as it was at 17 (yes it changes THAT fast) doesn't really matter.