At what age do most women become physically unable to have children?

Naturally, after menopause. So somewhere from 45-55.

The oldest I have known personally who had a child (naturally conceived and delivered, nothing wrong) was 49!

There have been women in their late 50s, 60s and 70s, but they all conceived through IVF. I think the oldest non-IVF mother was in her 50s, but I can't remember the exact age. Wikipedia has it.

Unable To Have Children

Most women are unable to carry a natural pregnancy by the time they are 48. If they do get pregnant, chances are, they miscarry. The rate of women giving birth to live babies at age 50 and over remains relatively unchanged for the last 80 years.

average age of menopause is 51, though some women get it sooner and some later. women typically experience declining fertility in their late 30s and steeply declining fertility in their 40s, so many women are unable to have children well before menopause.

There is no set age. Women are born with all the eggs they will ever have. When you run out of eggs you can no longer have babies. Whether you are 25 or 80. Physically there are not limits as long as the woman is healthy.

Well, a 70 year old women in India gave birth to twins not to long ago.

Soo, perhaps after 70.