Assuming that Uncle Jake is around sixty-five here (he actually looks older than that, but he's been through a lot, and may have aged prematurely), and that Petunia is about forty, and the standard in-comics answer for how long any decades-old character or characters have been around is 'about ten years ago', that would mean that the two hooked up when Jake was fifty-five and Petunia was thirty. That's not all THAT impossible - my parents know a married couple whose respective ages are late fifties/early sixties (I'm not quite sure) for her, and 85 for him, and they've been together long enough to raise a couple of teenagers. Love is blind, as they say.