queation? ladies help please!?

pardon me, im a guy.so, first of all i asked this question in not a pervert way. im just wonderin why my gf's is different. its like a of a kid or something..its like not fully develope or whatever..i dunno how to explain it..once again, not in a pervert way, i just wanna why..my friend told me shes just a virgin if her are like that..but i dunno.