At what age is best to have children?

DEPENDS. If your main interest is avoiding chromosome defects, the age is the early to mid 20's. There is a slight increase under 16 and it increases every year after the mid 20's. If your interest in being financially and emotionally ready for the work involved, the late 20's to early 40's may be better.All pregnancies have a basic risk of unexpected outcome. Reviewing risk with a geneticist helps some.