I've dated a woman in my life who was 19 years my junior and one 17 years my senior. And a few in between give or take 5/10 years either way. It really wasn't that different. If it's a mutually respectful relationship and her kin isn't forming a lynch mob then it's fine. Granted it's probably a rare thing to see a 20yr old young lady with a 45 yr old guy. If that rarity is a genuine loving attraction who's to deem it improper? I'm sure it happens once in a while for the right reasons. More power to 'em in those cases.