Strictly speaking IRL-wise here:

Let's say you're 60. The rule says the youngest person it's not creepy to be with is 37. I'm 37, and I can't say I particularly like the idea of 60-year-olds thirsting for me. ^_^; Not that I don't think some older people are attractive (though as an ace person I mean exclusively in an aesthetic/hypothetical sense), but that power balance issue still comes into play, not to mention an actual generation gap.

Maybe sticking to people within a generation of you is a better rule after the age of ~34? That's when "half plus seven" equals a ten-year age difference, and roughly ten years is what I'd consider a non-creepy, generationally compatible age difference between mature adults (cf. young adults and teenagers).

But again, that's me talking IRL-wise. When it comes to fictional characters, I agree with Ekwy. Don't talk about them like a creepy stalker or call them your husbando or whatever, and nobody will probably mind. {= )

~Neshomeh's most beloved characters as a teenager were older male mentors/role-models to make up for her alcoholic, emotionally unstable dad, and the thought of boning them still grosses her out despite being a fairly sex-positive ace.