Often our idea of how things should be is completely different than what the Lord has in mind. When I was younger, I never once imagined that I would not be able to have children. I figured I would marry the great guy (I did!) and we would work to build a great family (we want to!).
There are all sorts of calculations that take place in this world. As humans, we calculate the "right" age to make many of our decisions, but ultimately, and usually, there is a difference between those calculations and what actually happens. I figured I would be married by 22. I was married at 26. Sometimes the best laid plans fall short. That doesn't mean you stop planning, or just hand everything over to the Lord in frustration. It does mean, however, that you remind yourself that things are bigger than right now, that Rome wasn't built in a day, and that our sense of vision is limited. And, sometimes our calculations are different than His plan for us.