Depends on where you live, ect.
Additionally, it depends a lot more on circumstances than anything else, and who the two people are, who their friend groups are, their maturity, and which perspective you're looking at it from, as well as the genders... Shits fucked yo.
Basically though, its fine. And if its not, one of the parties can say that. If both think its fine, its fine. Some people might feel weird about it being someone who's in Uni dating someone who's in Highschool, but since they're just into Uni it can instead come off as kind of cool to have someone independent with their license to run around and take you places and all that sort of stuff. If the girl is younger, its sometimes also seen as good to date older guys because of mental maturity difference, though that does greatly depend on the people you're talking about.
As a general thing, its not weird. Some people will feel uncomfortable about it, but some people will feel uncomfortable about anything. Its not illegal, and it abides by the 1/2 age + 7 rule, so socially its fine.