Eh...I'm not a guy. But whatever, I got freedom to answer.
I thought guys had like this biology thing where they want to datum woman like their moms (an unconscious thing). Guys like to datum woman who are comfortable with themselves. In a sense, most guys actually like woman who are older than them because they got better confidence.
Though, I'm guessing with the change of society and stuff, it might not be like that anymore. So, here's an article:
link I don't think its gross. If they truly love each other, its very cute. If they're just together for the sex, its not really a relationship.