Just that, really, how long do you think is reasonable for someone to want to wait to feel "sure" about having a baby or getting married?
I'm trying not to give too much info away re ages or other factors in play, but let's say both parties are established adults with careers, finances in order, old enough to have had many relationships and know what they're looking for etc in life. Too old to need to play the field anymore. Certainly at the sort of ages where others would already be settled down/married/have children.
How long would you want to know someone/be in a relationship with them before you feel you're ready to take that step?