Son's friends are all girls

DS is in 7th grade and turned 13 on 9/1. It seems that since daycare, he has always had friends who were girls, which is fine, but lately in the past couple of years, it's like all his friends who he wants to hang out w/ are all girls. I don't want to make such a big deal about it. Occasionally I will ask him why he doesn't ever call a couple of boys who are in the neighborhood (walking distance), like Brendan & David. When they went to middle school, their school is so big that they are divided into 3 "houses" and they stay w/ the same kids in their house for all classes through 8th grade. Since David is in a different house, they never see each other, so I can understand that. On the other hand, he had made friends w/ girls who live on the opposite side of town, where I would have to drive him to their houses to see them, so it's not just the neighborhood thing.

It's not that I think he is going to be gay because he has had "girlfriends" in the past and talks about liking girls. He isn't that into either playing or watching sports, so maybe that is one thing that makes him have less in common w/ some boys. He is a smart kid & enjoys reading a lot in his spare time. He is also short for his age. He talks about being worried about high school cause he is afraid of being bullied (but I don't think that is happening now) and he hopes that he will grow. Since his dad is 6'1" and was short until 9th grade, I think that it is likely that he will be taller.

There's not much I can do about it and I don't want to make a bigger issue than I should as long as he does have friends. I just would like him to have 1 or 2 friends who are boys also.