I wasn't referring to mental disability, but aside from that, yes, a typical random person plucked off the street could generally learn quantum field theory, given about a decade of appropriate focused effort.

Mathematical maturity takes about a half-decade to develop, maybe a little more. Working through physics up to QFT takes a bit under a half-decade, in my experience. It's slow-going at first, and then accelerates.

I've seen people go through very similar transitions before.