I don't think a virgin vagina is tighter. More tense, very likely. But the vagina is made up of muscles. They can be stretched and they can lose their tone, but it takes something really traumatic like being torn in childbirth to do that. SEX WILL NOT MAKE A VAGINA "LOOSE." At most, when you become comfortable with sex (which generally hurts the first time) then you will be more relaxed.
I mean, does your throat become "looser" over a lifetime of gulping down food? No. Because it is made of muscles.
Your vagina is also made up of muscles. It is not a spandex thing that can lose its elasticity from being stretched. It renews and it gets stronger, if anything, from repeated flexing.
Vaginas, like penises, can be varying sizes. Like any other muscles, they can vary in tightness and tone. But the idea that getting fucked repeatedly stretches it is just not correct.
After childbirth, which can be pretty traumatic, it can be helpful to do exercises. The loss of pelvic muscle tone goes beyond how "tight" the vagina is and affects the ability to control urine. They're all tied in together. But if fucking will loosen a vagina in the same way, then we'd all be somewhat incontinent. Can you do a star jump, or sneeze, without wetting yourself? Then you are not "stretched" in that way. That said, doing kegals will increase the "tightness" of your vagina. But only in a different way.