Is it ok for an 18 yr old to date a 15 yr old? (plz read)?

Im 18 and theres this girl in my art class who im attracted to and ive caught her staring at me a few times, but im a senior and shes a freshman. I live in Indiana and the age of sexual consent is 16, pretty sure shes only 15, but theres also a closeness of age rule wherein if you're within 4 years of each other it is perfectly legal. Not illegal to date a minor in any state just having sex is illegal, and touching in certain places is illegal, sort of, Indiana is weird. So is Nevada, we have that in common i guess. But socially and morally do you see anything wrong with it? She doesnt look like a little girl or anything and she seems pretty mature. And im not just planning on having sex right away or anything, not just trying to "get laid", definitely would plan on waiting, even til shes 18 if i had to just wondering if people would think it was wrong, or how her parents might react? Ive known other seniors that have dated freshmen, i know its not unheard of, just not especially common. She's one of my sister's friends too, shes her age. Kind of a minefield here, thoughts? Also, are girls more attracted to older guys? Or am i just imagining things? She seems like she gets quieter when im around (i do around her a little too) and the few times ive talked to her she barely made a sound. Example: Said hi twice, she just looked at me, and quickly walked away. Another time i told her that my table was done with the tin foil (remember this is art class) and that she could take it, she barely mumbles and then walks away. Are these signs or am i illiterate?And im graduating in 2 weeks, but shes my sister's friend so she'll probly be over at my house alot over the summer. Also I'm responsible, just got a job, and im planning on going to college or maybe the army later on, not a scumbag here, just throwin that out there. me=pretty good guy.