This isn't happening. The average wait for a first gender appointment on the NHS to talk to someone is years long. In some areas, 10-20 years for any consequential contact.
Trans people aren't all autistic, or mentally ill - they're a tiny minority. Around 1 in 4 girls have been sexually assaulted and will experience mental illness. Autism is a totally separate condition and also affects a significant percentage of children.
And none of those conditions means girls and women cannot think for themselves. That is a simplistic, incredibly ableist statement.
Autistic people are often very relaxed and honest about gender dysphoria, and more likely to report it.
If your ableist argument held any water, then a huge percentage of kids would be trans. They are not. Maybe 1-2 per school if that.
The vast, vast majority of gender-affirming surgery being done on the NHS is performed on cis men.
How easy do you think it is to access any surgery? Waiting times are 22-44 weeks, with the NHS snowed under all year.
Most trans men don't have bottom surgery because they are highly aware of the risks. They aren't ignorant about this at all.
Gender-affirming surgery for trans people on the NHS is rare, most of it is funded privately.
Incidentally, if my son had pursued his career in ballet, he would have needed a breast reduction operation. And that would have been socially acceptable (all top-heavy ballerinas who want to succeed have them). I find that sick. Trans men making considered choices about their own lives is fine by me because it's their choice.
Cis women have gender-affirming surgery - on their breasts (for which the nipple is usually removed then sewn back on), faces, stomachs, necks, legs, arms...and so do cis men.
There is no epidemic of young people demanding top surgery on the NHS. Just a tired, weary cohort of trans guys who fund their own way and wish people would leave them the hell alone.