There isn't an age. The question around that is more about age of consent. We've had that discussion in our group.
Puberty does not start at a specific age for every person. There is a range, so I don't think there is a set age, but definitely, the specialist—I am not a specialist in this field—who treats these kids really wants to try to treat them way before they start puberty.
I'm just going to guess, probably 10 years in boys, and maybe younger in girls.