If it's any consolation, my childhood has continued well into my late 30s.

LIKE.
We have experienced this wistfulness many times. We feel it especially keenly, I think, with a child who is HG+ and also an only child. Some things, we 'skip' as parents, because of DD's need/desire for acceleration.
KWIM?
My 13yo effectively only has one more year of "childhood." Yes, this makes me sad. VERY sad-- for myself-- but on the other hand, I don't really have doubts that we've made good decisions with her. It isn't as though I'd change a lot.