I feel it is down to each person and as to when it suits you and your life.
There can never be a best time to have a kid and considering the costs!
For me personally the time we tried and it happened was when is was meant to be and God's will.
Like Olisa I had my two in my early 20s and so did my sister ,two and before turning 26. My dear sister is now a grandma and her daughter was 23 when she had her daughter last year.
Surely it must be down one to being fit, healthy and able. Plus there's the considering of one's body clock. No more for me I hope but as OH hasn't had the snip and as I still have the monthly I can never say no.