I am a RARE exception - mine could be felt, confirmed even by my midwife, at 8 weeks. For a while she suspected twins because of it but I've had my scan a few days ago and I just have one little bub in there! I seriously think that the majority of women feel it between 12-14 women, and then there is a smaller percentage of women who feel it before then and a smaller percentage of women who never feel it. I've been told by so many people I'm crazy for thinking I felt it at 8 weeks but I don't know what to tell you, it was there lol. Popped up above the pubic bone by an inch or two back then. I haven't checked since then, probably should because I'm almost 13 weeks and I'm curious where it is now. But just remember, even though there ARE average times for things to happen in pregnancy, every single baby and every single mother develops differently. Even in the same woman one pregnancy can be different from the rest, so you're asking for the average time when women feel it.
When I felt mine, it was hard and rounded, like a disc that came up above the pubic bone.