Maybe they get less superficial, maybe they develop a liking for bigger women, or maybe they just stop caring about what other people think and go for what they like. Or maybe they simply lower their standards (Which is a good thing by the way, because teenagers of both genders have some ridiculously high standards for what humans should look like)
I don't know what it is, but I've noticed that the older men get, the fonder they get of chubby women.
Obviously not all men like their women big, but all chubby girls can tell you that they get a lot more attention from guys over 30 years old.
Got the idea for the comic while I was waiting for a bus the other day and a huge woman walked past, and all the old guys couldn't take their eyes off of her, even though a woman with a perfect hourglass shape walked in the opposite direction.