I have mixed feeling about this too. I think there is always going to be a very fine line between assisting an upcoming athlete/competitor to achieve the best they possibly can and over training them with the possible physical and mental problems that come with that.
I think that for the majority of the events we have seen at the olympics that serious training will have to have started before someone reaches the age of 16. We have to put our faith in the governing bodies and coaches of the respective sports that their paramount concern is for the individual and their physical and mental well being, rather than the possibility of medals.
As to whether that happens all the time, well, I don't know.
Obviously in events that require a phenomenal amount of flexibility (gymnastics, rythmic gymnastics, trampolining, diving etc) the line is going to be even finer as training will have to have started in earnest before the age of 10. The ruling (iirc) that female competitors have to be 16 by the end of this year to compete is presumably an effort to prevent overtraining of very young women.
I wonder if the age limit is not there in the diving because of the reduced physical stresses of this sport compared with the gymnastics. Not sure how old the female divers have to be tbh.
With reagrds to tics and pre event routines, this is very common, in all sports. I remember having a lecture by the Arsenal physio. He said it was an absolute bloody nightmare if he had given a footballer a particular treatment or strapping pre match, and then they went on to score. They would ask for the same thing every single time after that as it was mentally linked to their success.
If you watch the archers or the competitors in the shooting events closely you can see they are doing all sorts of funny little things before they compete. I used to do a bit of archery and I tell you if I cleared my throat before loosing my arrow I always got a better score