physical activity stimulates muscle growth, the main factor contributing to increased bone density is calcium and D3 intake during the growing years along with thyroid hormones. and its not arrogance, its a fact that bone loss occurs and risk of fractures increases with age. im not saying he shouldnt be on the slopes any more than im saying older people should have other activities restricted. were i a doctor, id want to know more details before id be all for it. previous broken bones? arthritis? flexibility? does he think he'll be able to handle black diamonds lickity-split?