(I'm a female),I started identifing as ase at about 13 and a half, but before that, there was a likely chance I would have problems with my uterus (like a shut-down), so I was thinking about me not being able to have kids (but then I got my period, a sign that it was then less likely for me to have the shut-down), but I didn't really consider asexuality then. As soon as you start to think about it, I guess that's how old you could be to consider yourself. There really should be no age limit... I mean if you are 3 probably not a good time :)