Daughter was underage.
Depending on state, the fact that the boy was underage as well might actually make it not statutory rape.
For example, in North Dakota:
3. When criminality depends on the victim being a minor fifteen years of age or older,
the actor is guilty of an offense only if the actor is at least three years older than the
minor.
Florida:
(1) A person 24 years of age or older who engages in sexual activity with a person 16 or 17 years of age commits a felony of the second degree, punishable as provided in s. 775.082, s. 775.083, or s. 775.084. As used in this section, "sexual activity" means oral, anal, or vaginal penetration by, or union with, the sexual organ of another; however, sexual activity does not include an act done for a bona fide medical purpose.
Nebraska:
(1) A person commits sexual assault of a child in the second or third degree if he or she subjects another person fourteen years of age or younger to sexual contact and the actor is at least nineteen years of age or older.
We don't have the age of the daughter, so assuming she was at least 15, as long as he's under 18(and we know he was), it wouldn't be SR under the laws of North Dakota, Florida, and Nebraska*.
As far as I know, most state's SR laws have stuff like this. So, no, in general a couple of minors of the about the same age screwing aren't committing SR.
*I have been a resident of the above states, but I don't claim to be a lawyer, laws were pulled from state websites.