My son is 17 and he is uncircumsized, yet the skin on his penis doesn't cover any of the head. It stops just before the glands. Is this normal?

Maybe. Some men wear their foreskin in the retracted position where the glans, or head, of the penis is exposed. As long as this is not painful and he can easily replace the foreskin over the glans without resistence, it is probably okay. If you are stilll, worried, he should be examined by a local urologist.