I had all the children I plan to in my twenties, so I don't have a dog in this fight. However, there is a lot of oversimplification going on here, with risks for "older" parents greatly exaggerated. I know MANY women who had their first child in their late thirties/early forties without fertility treatments. None have had developmental issues with their children. And most have been able to have further children within a few years of the first birth.

And looking back in my family history doesn't bear out all the over-35 boogeymans either. My grandfather, for example, who graduated law school at 21 as valedictorian, was born to a 43-year-old mother. And many of the women in my family had children into their forties, because, I suppose, they kept getting pregnant.

Some of the fertility research is based on very old data. From an article in The Atlantic:

http://www.theatlantic.com/magazine/archive/2013/07/how-long-can-you-wait-to-have-a-baby/309374/

The widely cited statistic that one in three women ages 35 to 39 will not be pregnant after a year of trying, for instance, is based on an article published in 2004 in the journal Human Reproduction. Rarely mentioned is the source of the data: French birth records from 1670 to 1830. The chance of remaining childless—30 percent—was also calculated based on historical populations.

Other studies mentioned in the article concluded that 89% of 38-year-old women were fertile, and that most women do not lose their ability to get pregnant until sometime between 40 and 45.

If having biological children is extremely important to individual, waiting until 40 isn't wise, but it's not as risky as it's made out to be either. It's also important to remember that there are women in their twenties who have low fertility or infertility. We spend a little too much time browbeating "older" women, while ignoring older men and paying little attention to causes of infertility in young women.