I started when I was 3, Mom said i came into the living room wearing my sisters dress and stuff. but I don't remember that. Except that it was wrong for boys to wear girls clothes, or to hide it at least.
My first recolection was about 7 and trying on my sisters pantyhose. And 11 dressing up in my Mom's nurses uniform for halloween (i sneaked a pair of my sister's panties to wear underneath that).
Around 13 I started wearing my sister's clothes whenever no one was home. I have been hooked ever since