Sometimes the childless mate is content to be a "bonus parent" to the children of the other mate. If you’re over 40, how long to date before marriage depends on answering big questions.
This poses a great challenge to women who want to have children but know they’re limited on time and their pregnancies could be high-risk. It’s also common for men to want time alone with their wives before having children. They want to have children, but they’ve waited so long that women their own age most likely will have difficulty reproducing (unless they had previously frozen their eggs). This is one of the reasons that middle-aged men seek much younger women.
By the time they start thinking about marriage, women in their age range are usually starting a decline in their fertility in their mid to late 30s. Men, on the other hand, tend to delay their focus on family in deference to their freedom to "play" and to focus on their careers.