I've had 7 of mine since 25, and 6 since 30 :-). Der Prinz's fertility seems to be falling off afte 40, though; we have slightly more than two years between each of the last 3 children!
The only thing that kept my Mom from having more was a ruptured uterus with her 14th delivery.
She wanted more.
2 year interval is good. Keeps you from having too many in diapers at once.
I had 5 in 6 years....started at age 25 and ended at age 30. No pills ever, healthy kids, good father, wholesome family....all kids college graduates now.