Son is being very dangerous about this body in order to have his dream job.?

My son has always wanted to be a jockey. Since he was a child he loved seeing the Kentucky Derby. He has luckily been a small-bodied person, but not nearly as small as is typical of a jockey. If you dont know, jockeys are meant to be very tiny so the horse isn't bogged down. They are not allowed to weigh more than 112 lbs. At age 14 me and my husband allowed our son to begin injections by an endocrinologist in order to stunt his growth. He is still 5'4" now at age 20 and weights 102 lbs. 5'4" is not a desired height by horse owners so my son will have a very hard time finding a job as a jockey unless he is able to be on the lower end of the weight spectrum. Since there is now nothing he can do about his height, he is trying his best to get his weight down below 90 lbs. He has decided to donate a kidney in order to lose excess weight. I am very worried about this. He already shaves his body, eats 1.5 meals a day and takes laxatives on a daily basis. I am now worried my son's obsession will kill him. It cannot be healthy for him to artificially change his body in order to find this job. I have begged him to become a trainer but he said that doesnt fit with his goals. What do i do!? I am a loving and concerned mother!