Key points from article :
Average age of American mothers has increased from 24.9 years in 2000 to 26.3 years in 2014.
First births in women aged 35 years and over also increased by 23 percent.
Older age in mothers has been linked to a variety of adverse birth outcomes, such as multiple births and congenital disabilities.
But mothers who had their first child when they were 25 years or older were more likely to survive to age 90.
Multiple pregnancies also increases chance of living to 90.
The study was published in the American Journal of Public Health.