Hi! The best possible answer can give you only your endocrinologist, who knows your son the best. Just remember: there is no "normal" in medicine! There is only statistically median value, which also means that the individualy normal range can be very far away from this statistical median value. What I am trying to tell you is, is that it could be normal to have a spermarche at the age of 16 or even later, especially if taking growth hormones. One more aspect: if one mastubates, nocturnal emissions are unlikely. So maybe you could ask him whether your son does that and whether orgasm is achievable and anything at all comes out? If orgasm is possible, right afterwards he may obtain a urine sample and send it to laboratory for microscopic diagnostic to determine the presence of sperm in it. There is a condition called retrograde ejaculation, where seprm flows the wrong way- towards urinary bladder.