How long till your SO was ready to start a family?

I've been with my SO for 3 1/2 years which will be 4 years in May. We are young but I love this man with all my heart and I can't imagine spending my life with anyone else! I've been having baby fever for basically 2 years. It happened then it went away but it came back and I've been feeling this way again constantly for over a year now! I really can't wait to have a family but he's not ready yet and will say next June. He think's we are too young and he's just not ready yet and wants to wait till he's done training for becoming a Police Officer. He says he wants a family with me too but some days I just don't know what he wants because he acts like he just doesn't care.. When was your SO finally ready?! I just wonder if he'll ever be excited like me :(