@raphjd dealing with a person's mental health requires a level of a dynamism (AKA skirting age requirements when the benefits outweigh the detriments). That dynamism is vacant in your cookie cutter approach to age limits.
I'm not saying cookie cutters are bad... they work wonderfully for a whole lot of things.
There are very few things in society that should broach our standardized cookie cutter age limits that we have in place for things like voting drinking driving etc. trans care is one of them when it's done in capable hands, not the ones of the horror stories that you've heard about ...people who change their minds, they probably weren't in capable hands, unfortunately for them.
Just like people who die in plane crashes ....you would think gosh those planes crashing, that really should have been fixed by now..... yet they still crash... but each one makes us safer.