I have been deeply concerned about my brother. He's thirteen years old and even though it's none of my business, but shouldn't he be interested in girls by now? He is totally against seeing any magazines of women, doesn't like women showing off their bodies at all.

He is totally against sexual activity and usually I thought guys at that age would be curious about women’s bodies. I know no one’s normal, but to me this doesn't seem normal behavior. I have asked him if he was considering that he might be gay, but he is totally against people being gay also. I guess you could say I am a worried sister. Is there any advise you could give me so I wouldn't be worried anymore? And would he ever be interested in a woman? He says he would never be interested in those magazines and being curious.

It’s great that you love your brother and are concerned about him, but this is one area that I would urge you to stay away from.  First of all, there is no one age when boys begin to be interested in girls. Some bloom early while others do so much later.  But when young men his age do begin to be interested in sex, it’s not something they will necessarily want to discuss with an older sister.  You have a fully developed body, I’m sure, and he knows that he’s not supposed to get excited by his sister, and talking to you about sex might very well get him excited, and since he knows that is wrong, I can well imagine that he might be doing everything in his power not to have such conversations with you just in case it led to him having an erection. If he came to you with questions, that would be another story, but you shouldn’t be initiating these conversations. And you should definitely not be asking him if he’s gay. If he’s a late bloomer, I’m sure he’s already worried about his sexuality. Having his sister ask him if he’s gay is going to worry him even more. He might begin to think that maybe he is gay, when he’s not and the problem is only that his hormones haven’t kicked in yet. And if he already knows or guesses that he is gay, at thirteen I’m sure he’s not going to want to admit it to his sister, who might go running to your parents.
 
Sex is always a touchy subject, particularly with young people who haven’t become accustomed to their changing bodies. He needs his privacy right now, so my advice to you is to drop this subject. In fact, maybe you could try to reassure him, telling him that everyone develops at different rates and that he’s probably not gay, and that you’re not going to bug him about this any more unless he has specific questions, in which case you’d be glad to talk to him.