Been doing Parkour for about a year will turn 46 in a few months, not been training especially diligently, but learned the basics.
But i have spent the last month on a 4-5 time a week routine and feel great and plan to make it my primary fitness activity.
Not much of a stretch for me, i have kept pretty fit doing martial arts and fencing most of my life.
Mostly I have top learn how to be soft now, I weigh 180 pounds and am so used to throwing everything into my movements i have to really re-learn how to move and land like a feather.
pretty much just healed from spinal fusion surgery back in November (living hell) but Parkour is turning out to be a god send for me, marrying relaxation with fitness in a way that makes me feel alot younger and actually helps reduce my neck issues.
So don't sell yourself short 30 year olds i was competing in Jiujitsu at 38 with kids and i teach a 70 year old man how to fence and he kicks the crap out of 20 and 30 year olds regularly after driving 2 hours each way to train.
I envision myself doing this into my 60's or 70's
The Chinese martial arts teach you to keep your Chi flowing with relaxed exrcise as a fountain of youth and health, i beleive thats what happens with good Parkour.