My boyfriend and I have also talked about the prospect of marriage. He is currently in his first year of law school and I will start med school in the fall. We're both 22, going 23. Basically, we're waiting to be in the same city for the start of our new life together. (In other threads I've written about my Philly/NYC dilemma.) But, I'm almost positive I'm going to go to a school in NY and when my boyfriend is done with law school, he will try to clerk and work in NYC (his hometown).
We have a friend who got married following her third year of medical school. The couple decided to wait until then because it would leave the new bride time to adjust to being married since most schools give you 3-4 months of elective time that you can choose to do at another hospital.
I also talked to a couple of doctors and most of them said that you're going to be busy at any time in med school, just go ahead and try to do what you feel is best. There is never going to be a "perfect" time to get married and have kids between med school, residency, and attending. Just like there is not "perfect" time to start a relationship, things usually just happen.
The fellow in my lab got married while she was applying to med school and went to her one and only interview (she only applied to one school since her husband already had a job in Pittsburgh)... pregnant. She had the baby one month before school started and another one b/w her third and fourth years. She's currently in her last year of fellowing with two children and as she said, she's a young mother that made it work. (As a side note, she said it was hard but obviously, was very successful. Med school at Pitt, residency at Northwestern, fellowship at Children's Hospital in Pittsburgh.) It's very comforting to talk to her because she just gives you a realistic, personal aspect of how life can be as a physician, especially when both parents are professionals.
Anyway, good luck with your lifeplanning 🙂