I'm 55 yrs old and still go out Freeriding/Single Tracking/Urban Assaults on my Fisher Opie, live carfree and commute primarily on a Serrota T-Max that in mostly carbon fiber and XTR parts, and recently built a SS 29r Monocog for woods riding in Indianapolis (because there are no mountains here). I've also got a Santana Arrive tandem, a Salsa Campion with 105 parts, and a Fixie for local rides. I doubt I will ever stop riding until I can't walk.... It's just too much fun.
Fisher Opie Freeride/Urban Assault
Serrota T-Max Commuter
Redline Monocog