At what age(s) are you most likely to get pregnant? When are you the least likely?

Well there is two answers to this.

Most likely to get pregnant between the age you have your first period (12 ish) until around age 40. (Depending on the woman)

The ages least likely to experience problems with the pregancy/birth are different.

The best age (in terms of the least problems) is is from age 16 until about 32. Before 16 a girl often has physical problems with the birth. After 32 you are looking at eggs that arn't as healthy as they once where (AKA) more birth defects)

But it should be noted, if you are having a period you can get pregnant.

It is different with each woman. It depends on many factors including where you are in your cycle, and also your stage of hormonal development. As soon as a girl reaches puberty and has eggs that can be fertilized (some as young as 10-11 or before) she can become pregnant. In Africa and other cultures, there are girls in the age 11-13 age group who are pregnant.

Women have also become pregnant long after they thought they could. This includes women in their 50-60's. It is much less likely after the woman has hit age 50 or so, but certainly not impossible. Again, depending on the woman's hormonal system and analysis, she might be incapable of conceiving at age 45 or 48, while others could conceive as late as the 60's. I think there have been a FEW women in their 70's in the world who gave birth. I did not check the Guinness Book or anything like that.

Most:20-ish
Least: now

Peak fertility is not long after puberty. Fertility in both sexes falls falls thereafter. Women have the menopause, but men of that age are producing much less sperm of lower quality by the same age.

Least likely: From 0 to pre-puberty.
Most likely: around 17-23, I believe.

age 5