As a parent, who also talks to other parents, it may seem illogical but we worry more about our children in a situation where they are chatting in real life with "strange" adults than we worry them playing violent games. Everytime I am dealing with someone I know to be under 18 I can't help but wonder whether their parent knows or approves. This is a personal issue I have to live with but I don't think as a community we can dump all responsibility on the parents.
I agree that good rp is not based on the age of the player, in fact as an adult I probably find it harder to learn. The issue I have seen is more often the younger players have less patience for hanging back, observing and learning. One of the things I like about ps is the fact that it is not based on how fast my reflexes are. But if I spent a lot of time playing games in which that is the main focus, then if I wandered in to ps I would immediately be wanting that same experience.
Not to pick on just the younger players, there are adults who have a hard time adapting to the fact that they are starting as beginners with a character, that it takes a while to build the character up, and that a 16 year old may know a heck of a lot more when it comes to ps.
I think that as a fact of life we will always have the chance for good rp to be disrupted, by someone young or old, as unfortunately that happens in real life.