Hi everyone, I have a couple suggestions.
I would start by trying not to look at these kids like dickheads, problems to be solved, or anything deserving derision. It's just a bad mental state to be in, and doesn't in itself help anyone.
Sounds like they really get off on challenges and doing impressive moves. If they've never heard of parkour, they probably don't know of all the challenges and cool stuff you can do in the practice of parkour, and they're just left with tricks. Show them. That 5' precision is a great example. $10 says they came out the next day to work on it. Find more stuff like that - kongs to precisions onto a bench or something, teach them a dash. People like that often love challenges more than the rest of them, and there's plenty of those in basic, techinique-oriented parkour.
Definitely don't bother lecturing. The last thing a 14 y/o boy will respond positively to is a lecture by, well, anyone, much less an older dude they don't know. If it gets too frustrating watching, go off by yourself and let them be. It's hard to motivate yourself to train if you're frustrated while training.
If they're 14 and can already do every imaginable trick, they might make world-class traceurs someday. Bring them into the fold!