Surgically they can do them at any age, but you have a lot longer to do it before they get smelly, however they will give them a general anaesthetic, usually gas and air works well for smaller goats (is what my vets use for disbudding). If your vet is not that happy doing it, I would ask around for another. The danger of "catching" the urethra is real in small goat kids. My vet rings male kids during disbudding when they are under.