Need expert opinion on kids and squatting.

I have a extremely athletic 12 year old, who I was just told by doctor is going to be 6' 4"-5" and I wanted to get him squatting, which I feel is the most important movement/exercise for athletic performance.

Just wondering when's the most appropriate to start him on a program like "starting strength" or 5x5?

Thanks!

Need expert opinion on kids and squatting.