Parkour requires a lot of stamina and core strength. Two things i don't have. I used to be a lot more limber but years of inactivity and age have me at a point where attempting any of those moves would land me in the emergency room. I wish there was a Parkour group around my area. I would definitely join.
I was in the same boat as you. Last month I attended two parkour clinics at two separate gymnastics gyms. I had a great time, and really learned how far I had let my body go, as far as core strength, and limberness. Needless to say, the next day after each, I felt EVERTHING! The second time wasn't as bad, which tells me I've gotten stronger already. I have a martial arts background, and used to be a lot stronger, and a lot more limber. I want that back now, and will do what is required to have it once again.