Among certain cultures its common even among the more educated and Westernized among them. Among Pakistanis I see more than a few couples with an age gap of about ten years (always with the guy being older of course) and these guys tend to get married in their early 30s. In some cases its clearly an arranged marriage but not in others. They're very family oriented which means that all the cousins are pretty close to one another so you can get mingling between cousins of different ages. That can lead to an older guy being introduced to a younger girl through the friend circle of a younger female cousin.
I understand why some people find that odd, personally I am not really acculturated into that kind of thing so even to me it is somewhat odd. But I think that's completely different from some dude in his late 20s prowling house parties where he knows there are high school girls. These Pakistanis I know are unsurprisingly devout Muslims so its not like these older guys are out here trying to find a drunk 19 year old to bang, they want to get married.
The general path seems to be that they focus intensely on their studies and career and barely think about romance. Through their studies(sometimes undergrad but usually grad school) they might another South Asian Muslim and get along well enough to consider marriage. The girls rarely make it out without some dude snatching them up but for the guys if they get out of grad school without getting married then that's when they might end up getting married to a girl like ten years younger, sometimes even from the Old Country.
I wish my parents married me off when I was like 22 or whatever but alas they're not really like that.