I have read and enjoyed all the comments on here and I am probably going to earn the ire of all these fine guys by commenting. (I am not a professional pilot.)
At 18 I went for selection for a flying scholarship. My father was a pilot, my stepfather was a pilot and I went to a school where the RAF and flying were almost a tradition. After all the tests I was informed I was colour blind. Actually daltonic, just red/green.
I have had (and I hope continue) a wonderful life, a PPL and eventually built my own aircraft but reading the way the pilots who had the career of which I was deprived describe their lives makes me feel they sound like a bunch of spoiled brats. If they hated it so much why didn't they leave? Maybe the only serious regret in my life.
Three of my sons went the military route. One is out, one comes out in a couple of months, the other may stay in, or not. I have to say they have all gained life long friends, something they didn't do at school or at college and their training, while frustrating at times, has been outstanding.
If your son really wants to fly he should find a way and you should support him but do not go into debt for him. I didn't, I wouldn't and neither should you. He wants it bad enough he'll do it on his own.