My 7 year old (high functioning asd) son wants to be a girl

Hello all, new to this site and this forum,
I have a beautiful son who is 7 years old and has a diagnosis of high functioning asd. He is very intelligent with an almost photographic memory and a as is the case with high functioning asd he is a logical thinker. Ever since he was two he has preferred to be in the company of girls & women to boys and men. I think he prefers higher pitch voices to lower pitch ones. Also i know he likes long hair and pretty clothes as they are more asthetically pleasing for him. The thing is that he really wants to be a girl, he says this to me, he has been saying it since he was 3- for four years! He knows about anatomy and says he want to have a vagina and that he wants to have a womb when he is a woman so he can have a baby. He also want to wear girls clothing, we have constant battles about what he will wear, i try to compromise with this, for example he wants to wear a skirt so i bought him a kilt. He attends a school for children with asd and they are unsure of how to deal with him wanting to be a girl but they will not let him wear his hair in bunches (he likes it in bunches) and they say that he already has a hard time socialising and if i give in to him wanting to wear leggings etc then it will make his life harder. The thing is, i have no problem with what other people will say, to be honest i don't give a hoot if my boy wants to wear even a dress, what i'm not sure about is how much of this is obsession to do with autism and how much of it is just my son. I know of no-oneelse who has ever experienced anything similar with a child with asd.  If anyone has any experience of this, or can give advice, please please comment
Thank you so much for your time