Individuals being below the age of consent is the pivotal issue here. No adult has the right to take advantage of a minor in this fashion (yes, I recognize that chronology is not a fool-proof determinant of maturity, but it is valid enough to have served as a legal standard in nearly all societies throughout history, though the specific age chosen has varied substantially). Given the usual inconsistency between sentence and time served, the 30 years of awarded punishment were probably assigned in order to generate the 5-6 years some of you think to be more fitting.

Consenting adults? Different issue entirely.