Trans youth can access HRT, and in some cases surgeries. The only age-related requirement in WPATH v8 is that puberty has started, there’s no need to wait until 18.
For reference cis people typically start puberty around age 11, though 8-14 is the starting range.
Never heard of anyone who had a gender dysphoria related surgery before the age of 18 ever. Nor did I ever hear from any endocrinologist who started HRT before the age of 16.
The gatekeeping from medical professionals is massive, there isn’t a single professional who doesn’t question ones identity 20 times during the course of months just to be sure.