@vampkittyvv if she was reincarnated as her previous age (teenager), then mental age is no longer an issue.
I concede that the author left her feelings intentionally vague at the beginning, iirc something like "if it were me I'd make him happy." Up to your own discretion if you feel she's self-inserting into the heroine role or not. So any romantic intentions are unclear.
Either way, she definitely took on a nurturing role that she (arguably) held on her own since no one else did this. She taught him a lot of things not strictly academic e.g. interpersonal relationships. Although he was the "master" in the relationship, she saw him as a pitiful, powerless child and often said no, reprimanded and taught him to fix his mistakes. She looked after him when he was ill and cured his curse which was his major ailment. She became the only person he could depend on when most everyone else shunned him.
As some people have stated, it would be the equivalent of a babysitter who, after an absence, came back and dated the now grown child they once reared. It's not illegal, but it's an uncomfortable topic for some and not one that has clear right/wrong rulings.
Personally, I'm not dropping the series because of an age gap issue (I'm willing to suspend disbelief as is necessary in a lot of isekai/reincarnation series) but because she's a dull character.
Just wanted to discuss the reasons why some
might have issues with the pairing because as we've demonstrated, it's a quite a contentious topic with nuances that shouldn't be reduced to "she's a pedo" "she's also a minor".
As an aside, just because something isn't uncommon, doesn't make it right e.g. littering, tax evasion, taking food from the fridge that isn't yours.
Whoah! That's long, but great discussing with you