I don't think anything ever caused me to crossdress.
My mum did reveal to me early on in life (years before I first 'borrowed' her clothes) that when I was a baby up to the age of 2 she would dress me in girls clothes.
Not to take me out in or anything like that, but she used to knit and sew clothes for my female cousins, and she needed a willing mannequin of the same size.
That's where I came in LOL.
I still don't remember any of this, even to this day.
In terms of when I started to realise I liked it?
Well my dad was always around, so it wasn't for lack of a male role model.
But there are myriad theories, loner kid, bullied, never had a GF until I was 17 (started age 13), the kids in my street were mainly girls so we would play together a lot.
I dunno, I just kinda wondered what it felt like to wear the clothes that girls and women wear.
One try and I was hooked.
