My first fursona was... well, I didn't exactly realize what it was, because I was 7 at the time with all my 'make believe' pets and selves. He ended up being named Hunter, and from the time I can remember was always a wolf, but in my mind a separate part of me.
I guess over the years it evolved, but I never really got the connection between my 'friend' and 'me'.
In the end I finally found out that my other-self could technically exist, or rather, the time I figured out what a persona was.
My current fursona took a bit of time though, and I can barely explain how it came around. I knew it'd be canine, and have glasses, and probably wavy hair and fluff, but the orange and blue? I have no clue where that came from. Either way, it's stuck, and sense then I've just taken it as it was; evolution.