Mental performance is the single most under-utilized tool in sports. Colleges want players with mental performance training.
This is not for everyone. Only the serious athletes that aspire to play at the collegiate level or higher should consider individual mental coaching. Mature athletes 13 and up are considered. If professional mental coaching isn't for you (or your child), still practice some sort of mental training.
The short answer is NOW! Training in the off-season, pre-season and in-season is important as we use a structured process for the different seasons that the athlete is in.