Sharon Jayson has an excellent article in USA Today about the debate over what is the best age to marry. The marriage age has been creeping up and averages the highest ever -- nearly 26 for women and 28 for men. Everyone agrees that you shouldn't marry as a teenager if you can help it, and most agree that you should start having kids by 30 if possible.
The division among the scholars in this debate is between Norval Glenn, who found that those who marry in their mid-twenties are happiest, and Andrew Cherlin, who argues that those who marry in their late 20s or early 30s are the most mature and settled.
I side with Glenn in this debate. I think having children is important to the great majority of married couples, and delaying trying to have kids into your 30s is dicier than most people know.
I was struck by another point in this debate, though: everyone in it assume that marriage should come before children. This is a debate among people on the upper side of the "marriage caste" divide. For those one the lower side, where single teen mothers are the norm, 40 is the ideal age for marriage, whereas 20 is the ideal age for motherhood. This is the further reason I side with Norval Glenn. He holds out for the crucial connection between marriage and parenthood. Separate them, and the social fabric unravels.