Back to the topic for a second... for me, I started cross-dressing when I was 5.
To be more precise, I'd worn girls' clothing pretty much from birth because my mother was so enamoured of the idea of her 'pretty blonde daughter' that she'd always dress me up in frilly girly stuff. Every photo of me taken before the age of 5 shows me dressed up like a human doll.
But at the age of 5 I started to notice gender differences between boys & girls, and I realised to my horror that everyone was lumping me into the 'girls' category when I knew I should be in the 'boys' category. I told my parents straight away but of course they denied it. I wore boys' clothes wherever possible (usually my brother's old hand-me-downs) but I was forced to wear dresses for my school uniform, and my mother would force me to wear dresses if I wanted to attend any parties.
From the age of 5, wearing those dresses felt, to me, like cross-dressing. It ended when I refused to ever wear women's clothing again.