Rhapsody said what I was going to say, only better.

12-year-old boys are most definitely thinking about sex, and even younger. But I truly doubt he finds his mother's stomach a turn-on, but rather he doesn't want his mother dressing provocatively. Even if he's the only one who sees, he doesn't want to think of his mom as being a sexual being, a person who desires sex.

As for your concerns over your attraction, I can't say whether you're a lesbian or not. I absolutely get aroused by some male bodies. Most women do, but most women aren't attracted to all male bodies. Some women like thin men, some like fat men, some (like me) like a man with muscles...it depends on the woman. But just because you don't find the male body in general appealing doesn't necessarily mean you're a lesbian.

Do you find women's bodies sexually appealing? Do you fantasize about having sex with them? That would be a better clue. Do you have any sex drive at all? If not, you may be asexual. A lack of sex drive can be due to something psychological and/or physical, and may be treated and possibly cured, but I'm not saying that you're having that problem...or any.