Even better, your friend's boyfriend could easily go to jail. Here is a discussion of the age of consent laws in your state.
****************
Missouri
The age of consent in Missouri is 17.
Mistake as to the age of the victim may be a defense in some circumstances as defined in RSMo 566.020.
Statutory rape and sodomy, RSMo §§ 566.032 and 566.062 involve a child less than 14 years of age. Statutory rape and sodomy in the second degree, RSMo §§ 566.034 and 566.064 involve a child less than 17 years of age and an accused who is 21 years of age or older. The crime of Child molestation in the second degree, RSMo § 566.068 , occurs when a child less than 17 years of age is subject to "sexual contact".
The distinction among those crimes has led some to the false conclusion that Missouri has a close in age exception. Missouri has no such exception beyond the degree of crime committed.
While the statutory titles are cast in terms of Rape and Sodomy, the statutes prohibit conduct that is described as "sexual intercourse" and "deviant sexual intercourse". Those terms are defined in RSMo § 566.010.
Statutory rape, second degree, penalty. 566.034. 1. A person commits the crime of statutory rape in the second degree if being twenty-one years of age or older, he has sexual intercourse with another person who is less than seventeen years of age.
Statutory sodomy, second degree, penalty. 566.064. 1. A person commits the crime of statutory sodomy in the second degree if being twenty-one years of age or older, he has deviate sexual intercourse with another person who is less than seventeen years of age.
Child molestation, second degree, penalties. 566.068. 1. A person commits the crime of child molestation in the second degree if he or she subjects another person who is less than seventeen years of age to sexual contact.