I normally don’t answer questions unrelated to gay trans men (or even trans men in general), but this one I felt should probably go up.

Yes, there are ways to curb testosterone production in teen cis guys.  However, this isn’t something that should be done without a good reason.  Actually, I don’t think you’ll find a doctor who will do it without a good reason.  It’s hard enough getting them to prescribe hormone blockers to young trans women.

I don’t have the knowledge required to go into this in much detail, especially not without knowing why the person in question wants to slow their/their son’s hormone production so all I can really say is talk to your family doctor.  If it’s for reasons relating to gender identity there are support groups to help you figure things out.  PFLAG has a trans-specific group called T*Families, the local chapter should be able to point you in the right direction.