Does everyone have the same level of intelligence? Are you really telling me that absolutely any member of the public could learn QFT, even people with a severe learning disability and low-IQ? Anyone you just randomly plucked off the street? Just no.
This doesn't mean that there isn't value in an adult choosing to learn an instrument (i.e. study physics). It can be enriching even if one never reaches the point of quitting their day job to play music full time.
Don’t get me wrong, I completely agree with what you’re saying. In fact, I encourage anyone with even the slightest inclination to study essentially anything, but especially physics, in their own free time to do it. You’re spot on in saying that there’s value in doing that.
The only assumption I wanted to challenge was that absolutely every human on Earth could do it. I just think that’s patently untrue, and betrays an inability to view things from other people’s perspective.
How many people with Down syndrome have mastered calculus? Let's please attend to reality in these matters.
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.