Sorry for the long delay in responding. For the most part it is pretty hard to over train a 14 year old who is in pretty good shape. Especially if it is only for a few months. Typically it is harder to get them to do any training at all as opposed to doing too much. But with that said, look for signs of fatigue. Restless sleep, loss of appetite, general fatigue through out the day. Check out this article for more tips.http://www.racerxvt.com/article/overtra ... all-victim
Hope this helps and sorry for the delay.