Hi, what is the biggest age gap between children? I'm 35 and have been with my partner for 17 years. I have a daughter from a previous who is 18 in a few months. OH has no children. Lately I have felt that I have left it too late to have another child as the age gap would be too big and it would feel like parent and child for my daughter rather than sisters. But I have this longing for another child that I want to have with my OH and to give him a child. Its something we've never talked about and the years have just passed. OH adopted my daughter so as far as hes concerned, she's his. He raised her. Now I feel like I have left it too late for us to have more children.