Big Nikki here.
I think Learning has it right: wait a year (or two).
Yes age matters, both for safe fertility and for the parents to be robust enough to good vigorous child-raisers.
But you don't want to be too young -- parents, I think, should have a nice handful of years to relish adult life before children. And a relationship should best have some mileage on it too.
Yes, younger is better for childbearing. But would one year or two years matter as much as a year or two of your relationship settling in?
Ask yourself that question, and I think your answer, either way, will guide you well.
-- Big Nikki
PS: John and I are busy doing the nasty (scratch that, doing the nice) to make our first.