This is definitely a tricky subject. One one hand, it's far too common for parents of a transgender person to be entirely against providing their child with what's necessary. On the other hand, it's out of the question for a non-adult to make adult decisions. The most black-and-white answer I can provide is that, yes, they should wait until they are an adult to make that level of decision. Luckily, hormone treatment can help a lot up until that point... which is also blocked by far too many parents who do not want to understand. That's probably what needs to be addressed more immediately.
I also think there may be some merit to Bella's point.
I also think there may be some merit to Bella's point.