Reminder: If your son reachs twenty years old without sexual intercourse, it's better to take an appointment to make sure everything is normal. Otherwise anomalies that could have been revealed thanks to a partner may be kept dangerously secret.
A quick exam consisting in :
1) global visual check .
2) evidence of no erectile dysfunction.
3) balls quickly back to their round shapes after two minutes of pressure, sign of normal production of semen.
...will potentially allow diseases to be treated if caught early. If the exam is not done before twenty-four years old, some minor treatments are not totally reimbursed, so better not wait too long.
Of course if you bump into the Doctor or if she is a family's friend, it's better than months on the waiting list !