Hard to say but to back his claim that he was programming since the 90's his CV shows he was working on stuff that's clearly more than your basic undergraduate skill level since the early 2000's. I'd be willing to bet he has more years under his belt than most HN users. I mean I'm considered old here, in my mid 30's, and this guy has been programming most my life. Though that doesn't explicitly imply experience, or more specifically experience in what.

That said, I think people really under appreciate how diverse programmers actually are. I started in physics and came over when I went to grad school. While I wouldn't expect a physicist to do super well on leetcode problems I've seen those same people write incredible code that's optimized for HPC systems and they're really good at tracing bottlenecks (it's a skill that translates from physics really really well). Hell, the best programmer I've ever met got that way because he was doing his PhD in mechanical engineering. He's practically the leading expert in data streaming for HPC systems and gained this skill because he needed more performance for his other work.

There's a lot of different types of programmers out there but I think it's too easy to think the field is narrow.