Should be a four letter word.
Seems like we all say it at some point (I know I certainly have)... I regret not starting to try sooner.
In my current (more sane and peaceful) mindframe, I can see that this is dangerous thinking. Should I have tried to get pregnant when I didn't want a kid, just in case I did someday? Should I have brought a child into the world to be parented with that lying, cheating douchebag I was living with when I was 21? Should Prof and I have jumped into marriage and parenthood while we were still in school, living in different countries?
You just can't make yourself want something you don't want. You can't force yourself to be ready for something. Sure, you can step up and deal with it if it happens unexpectedly, and you can even grow to be happy about it. But when you have to make a conscious decision to start down the path, it just seems ill advised to do "just in case" the future might not work out the way you think it will. You do the best you can in the moment and try to look at mistakes as educational opportunities.
Just like parenting, I expect.
We can't plan for everything. We can't see the future. And every past decision we have made, every path we have chosen, has contributed to who we are today. Baby-making situation aside, we have a great life.
Do I regret not starting to try sooner? Occasionally, in darker moments... of course. I'm only human after all. But on the whole, no regrets.