I'm not sure when I became a grown up gamer.
But I can definitely see the difference between the maturity I had when I was in my teens versus now.
When I was younger I was a a troll, incredibly vulgar, and just a downright terrible person. I was the guy who'd be killing themself -- losing points for your team. I'd be betraying you in Halo. I'd be the impersonator, the manipulator, the instigator and it never ended well. I enjoyed that part the most.
Whenever that completely stopped -- thats probably when I became a grown up gamer.