When you're ready, in my case, 30.
I read the average was 30yrs, but I don't believe there's a right or wrong, maybe too young or old, but I wouldn't know how to judge that, being a good parent isn't determined by age alone, but personally I am glad I waited until now, I can devote all my time to my children, my life is now intwined with Isaac and however many siblings follow, I don't feel I have things I've not done, the things I want to do now are with my family, and I have a good relationship with my OH (not to say you need that either but for me I wanted that).