I don't think it's wrong at all for you to like someone who's a couple years younger than you. But I don't really think you should try to have a relationship with this boy or anything, I think a few years younger than 16 is a little young for a relationship.
Nah. I have a friend who dated a girl who was 14 and a freshman when he was 16 and a junior. An age difference of just a few years is common and not a big deal, especially if the younger one is mature for his/her age.