The question of how young is too young to begin Performance Training seems to come up quite frequently. I will address it very briefly with three points. Side note, I am contemplating turning this topic in to a lengthy article because how vital this topic is to fully understand.
Three of the most common mistruths I have personally heard:
Kids can't lift weights, it stunts their growth
They do not need to do it, they develop on their own
Sport specific training is more important
Answers to the mistruths:
1. Wrong, incorrectly lifting or overtraining with sports can lead to injuries; sometimes this can mean fractures to the growth plates. However, overloading the musculature system is a great way to increase muscle spindles and, in a simple way of putting it, create an intelligent highly active muscle. Kids, just as untrained adults, should be taught how to move with efficiency and as their level advances, so can their weights.
2. This argument no longer holds merit in this century. The modern world has lead to less developed kids... with a drastic reduction in outside activity away from their organized sport(s). Computers, video games, cell phones, and other tech devices is keeping kids inside with less laborious activities. In addition, creating 'sport specific' athletes at a young age has increased the rate of imbalances and injuries. Performance training seems to be the best solution to less developed young athletes.
3. It is better to create an athlete then a sport specific athlete at the younger ages. The best athlete will always thrive in every sport (speaking specifically to the high school ages and below). Therefore, if you work on developing the athlete first then you will increase their ability to perform in their sport. Adding more sport specific over performance work means you are taking care of the body / mind that is used to play the sport.