He may be a late bloomer, and he may be *PLEASE EXCUSE THIS NEXT THING I CANNOT THINK OF A BETTER WAY TO PUT IT* “a grower instead of a show-er” for a lack of better terms meaning *IM SO SORRY FOR SAYING THIS* when he gets older...his erection may grow into an appropriate size. I know a few people like that. There could be a medical reason why, but it could also be genetics.
I think we should not be worrying about our sons' penis sizes personally. I have two sons. They have a doctor who gives that area a look see each year at their physical and will let you know if something is irregular. But worrying about how large either of my son's penises are erect is not on my radar as a parent.
I'm trying to figure out how one of his sister's hairs got wrapped around him. Oh boy, that sounds unusual.
Well, yes. Agree with rockrose that you should make an appt. with his pediatrician. Ours does well checks every year and checks that area quickly.
good luck
Has he had regular medical checks? He should have had a pediatrician check recently where they checked his genitalia.