Preface n = 1, and I didn't read but thought I would share my observations of my friends/classmates.
All the older guys in my class can find dates all the time (match.com, bars, etc). They have no issues since their clocks aren't ticking, in addition to the fact that a future doctor is a hot commodity. Nurses and drug reps DROOOOOOOL over the male med students at my institution (and I bet that is universal).
All the older girls in my class have a harder time since there is more pressure on them, and while its certainly anecdotal they usually have higher expectations. Further, in some of the busier residency programs that I have rotated with, most of the girls are single or in fleeting relationships, meanwhile all the guys are married. Some of the cushier programs (FM) the ladies are engaged.
The interclass relationships are usually rocky but some stick it out and are even long distance. I can't imagine the stress of having to couples match, see each other at random times, etc.
For me personally, I recommend and have enjoyed being with someone not in the medical field and has a life outside of me. She understands I am busy, but is committed to having a healthy relationship. When I come home, I like to hear about her day and am thankful its not about more patients.
Lastly, there is PLENTY of time to have a relationship and date outside of medicine. Certainly the early part of residency will be hectic but if you don't make time for stuff, like a relationship, outside of medicine you will burn out.