Sorry for some of the responses on here, some people can be rude and cynical due to what goes on around here.
Anyway as for as I know there hasn't been any studies done on teenagers going through puberty using dutasteride. As for your concerns about using the topical so it doesn't go systemic I'm afraid it wont help, most vehicles aren't made to keep drugs located in the dermis. Dutasteride stops the creation of DHT in the body by a very large percent. The issue with that in regards to males under going puberty is that DHT is important. I would be weary about putting a guy on something like that even if its a low dose. Also dutasteride along with finasteride can inhibit certain neurosteroids in the brain that can cause side effects in some users such as depression, brain fog, and lack of rest full sleep.
Honestly in your son's case minoxidil alone probably wont help him but it is worth a try. If anything try a low dose of finasteride before dutasteride. Dutasteride is considered a last measure when nothing else works
Thanks so much for a well considered response. It is nice to know someone sees my concerns thoroughly. I'm keen to find out more about the zinc spray developed in Sydney someone suggested. In all the circumstances it could be a better option for my son.