Honestly? It's not that deep at all.
Gross? Maybe, depending on the reader, they might find it personally gross. People can act weird when it comes to sexual things, even at the hint of such, which I think is a major problem in society.
Sexist? Lol, no. Yeah sure, the girl being turned on by the strong guy might be a trope but its a trope for a reason. People (Yes, not just women, men too) are attracted to strength. That's natural. Being turned on at that age is perfectly natural as well. Source? Me, literally. I was once that age. Puberty turns people into a mess and our hormones are usually out of wack. Yeah, you might be uncomfortable by the fact that someone at that age actually experiences such feelings/Emotions (And that's fine) but its a fact that you shouldn't ignore/deny. Being ignorant only causes more problems in the long run.
I think the fact that your novel addresses such things is a positive and I'd even encourage more novels to do the same, whether through immature jokes or through a serious lens.
And at the end of the day, it's purely fiction. So anything goes, really.