if he's fighting this Wednesday, in 2 days, then do no extra cardio. he won't have time to recover for his match. but after that, you can consider picking up the cardio, starting maybe with some short distance running, some sprints here and there. not much more then twice a week on off days from the gym. as far as strength training, ya, being that young it is best to only stick to bodyweight exercises, and nothing too taxing. again on off gym days.
his body will be growing a lot in the next while, and that provides enough stress on the ligaments and joints, musculature of his body, without the added force of outside elements. in short, take it slow and easy, add a bit at a time. it'll likely help keep him from getting too bored of it also, which can come quite easily from over training.
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