Full Disclosure: I am not a feminist; at least, I don't believe I am.
But I think you're taking a slightly male-centric tack when you say 'in regards to the same starting point'.
Like someone else has pointed out, women have a shorter fertility-span and yes, there, it is the instinct and the hormones and what-not that make them more predisposed to having kids.
But I'll tell you, if there was a situation so that women could start families whenever they wanted, there wouldn't be such a generalisation across the board.