To be a parent or to not be a parent. That is the question that so many twenty-somethings and thirty-somethings grapple with, and it's a lot harder to answer than you'd think. Of course, some people don't have a choice in whether they become parents. Babies sometimes just happen to people, and that's that. But for those with the privilege of family planning, it's all about the timing. Some people want to have kids as soon as possible, and some have to scramble toward the finish line, with the s…