Yes some were under. Here's NY law: In New York State, a person who is under age 16 but older than 13 years old can consent to sex with a person who is no more than 4 years older; the crime of the 3rd degree rape only happens when a person over the age of 21 has sex with a person who is under seventeen years old or younger and that person can or may be punished with up to 4 years in prison. The younger the victim is, the more severe the punishment. Note that this mans if you are 13 years or younger, you cannot legally consent, regardless of whether the other person is the same age or not.
Andrea Costand's defense is that he drugged her and drugged people can't give informed consent. Cosby's defense is that the women didn't say no or some such thing. Cosby admitted drugging the women before the sex acts, what kind of freak does that? I'm sure he could have had "awake sex" with any women he wanted. In fact he told a fellow comedian who was just up and coming that once the guy got famous he'd get so many offers of sex that he'd need two d*cks.
Cosby's a sicko, a pervert and an adulterer.