When I was a kid, long before Parkour was a thing, I thought I was going to be a stuntman when I grew up and loved jumping off of things.

When Parkour got to be a thing I was in my late 20s, I got involved and went hard for several years. I could drop 12 feet to pavement no problem.

Nowdays I'm into bouldering, still taking big falls, and my knees are fine. Knee cartilage is a living tissue that responds to stimulus and can be built up progressively over time.

Parkour is much safer than it looks when done with the right approach. In field sports there is a lot of unpredictable things that can cause long term knee injuries. In parkour everything is very controlled. When you see a traceur doing a big trick, they're just doing bigger variants of maneuvers they've practiced hundreds or thousands of times before at slower speeds and closer to the ground.