At 14 I was 5'7" and just over 100 pounds.  Now I'm 6'1" and 145.  That boy gained more weight in less than a year than I did over several years as I put on another half foot of height. At 15 he should have known better unless he had a mental disability of some sort.  (Quite possible with genes from someone who actually believes that weight is genetic.)  If he was too stupid to understand the simple fact that his diet was causing weight gain, then it's child abuse.  If he was smart enough to connect the dots, then he's too stupid to be allowed to reproduce.