30 and 50. Everyone's fertility is a little different, but it is possible to detect about a 10% decline in fertility rates in women around age 32. By age 35 a woman's fertility is half that at age 20. For men the effect happens later, around age 50-60. Differences in health history have significant effects on this, so check with your doctor for your personal fertility evaluation.
Early for women. For women at around 30 years of age, while men in the 40-50s. Having said that, very rarely women conceive after age 44, while men can conceive well into the 70s.