This article by Blane is worth re-linking here: http://www.parkourgenerations.com/article/dilution
The entire thing is well worth the read, and although it is aimed at traceurs I believe much of what he says can be applied equally to other physical disciplines. Only going to directly post the summary at the end of the article here.
1) If you're new to Parkour, research as much as possible and learn from the people who have walked the path before you, but do not lose your creativity and ability to think for yourself. Try new things, explore different methods and progress at your own pace. What you need to remember is that the people before you have more physical experience that has built what I refer to as 'granddad strength' and that cannot be taught or passed on. You can rush the theory but you cannot take shortcuts on the practical stage if you want to last in this discipline.
2) If you are more experienced in Parkour and feel like newer people are better than you, do not feel pressured in to pushing yourself too hard or doing things just because they are. Try to warn them of the dangers of trying things beyond their bodies' conditioned state - even if they can do something, doesn't mean they should. They are learning faster than you due to the wealth of information before them, due to your hard work.