Question is who is allowed to date them without getting a visit from the police.
Assuming the theory that they are the old ships made flesh, then Kamikaze was "born" in 1922. Kancolle seems to take place in the present day or near future, so by that she's approximately 94 years old. Going just by that, it's Kamikaze who shouldn't be allowed to date anyone below the age of consent.
But between construction as a ship and construction as a shipgirl, there's the great length of time she was effectively dead after she was scrapped. If "aging" stops at that point, 1947, and resumes after being reborn, she's closer to 25. Which still puts her out of range to date anyone who looks her age, but safe for anyone older. Don't expect a lot of support for an older male dating someone who looks so young though.
There's also the possibility that they measure her age as when she was reborn as a shipgirl, in which case, she's like, 1 years old. That sounds silly, but it does raise up the question of if she's old enough to qualify for adult civil rights. If they treat her as just being born, or treat her as her physical age suggests, then she's a ward of the state, a child for all intent and purposes without voting rights, control of her financial and property assets, and presumably very limited in what sexual activity she's allowed to partake in.
And of course, the obvious: If she looks like a younger teen, acts like a younger teen, and for all intent and purposes is a younger teen, then should she be legally a younger teen? Child soldier aside, that limits her dating options to boys in the same apparent age group, maybe a few years older.
