I think that depends on how much you base this in reality. Even if we say it's fiction, there are still many things we base on reality (but how much depends on the genre and story). For example, in the story, humans are still homo sapiens and behave like irl humans.
Same with the age gap. The story never specified that the young ppl in this story is more mature and wise than irl kids, so a lot of ppl also base how it'd feel for 2 ppl with such age to date and they find it weird.
If you don't feel weird, then it's either (1) you didn't base it with reality and imagine the kids in the story to be much more mature and developed than in reality, or (2) you don't feel weird irl too.

Ppl who don't find this weird or defend this could be because they're too young to get it. I was like that too. Couldn't imagine what's wrong because I thought at the age I was, I was already grown up. Boy was I wrong.
For easy reference, imagine a 3rd grade kid with a high schooler. It's that weird. They're definitely not in the same headspace and maturity. Kindergarteners greatly differ from Grade schoolers. Same thing for Grade schoolers and middle schoolers, and high schoolers and college kids. These are the small age gaps that change people.. from kids to teens and from teens to adults. It's really huge.