I just realized, if Henry doesn't get killed by something, he's going to live a really long time. Like, stupidly long.
He's a druid and at 18th Level he gets access to the class feature Timeless Body, meaning that for every 10 years that pass, his body only ages one year.
He was mid-thirties when Odyssey took place, it's like two and a half decades later and biologically, he's only now in his late thirties, maybe forty at a push. He probably looks more like Lark and Sparrow's brother than their dad.
Also I fully believe that Henry wouldn't think it was magical in nature, he would be totally convinced it was due to lifestyle choices.
Glenn - Henry, look, here's a picture of us from twenty years ago. And here's a picture of you I took earlier today. Side by side, look, you look exactly the same.
Henry - Well, would you look at that? Gee, it looks like wearing all that sunscreen is really paying off!
Ron - Okay but you're sixty and your hair isn't even thinning.
Henry - Huh, I guess you're right. That's probably the all natural shampoo that Mercedes makes - she puts rosemary oil in it, she thinks it smells nice, but it's also supposed to be good for hair follicles. I guess it's working?
Darryl - Henry, everyone else your age has creaky knees and back problems and groans when they get up out of a chair!
Henry - Ah, yes, but you're forgetting I do yoga every day, so, that keeps me limber.