We use data from the National Incident-Based Reporting System (NIBRS) to examine the effects of age on the risk of sexual and physical assault in prisons and jails. Our evidence suggests that male inmates of all ages tend to sexually assault young men. The preference for the young is much stronger for sexual than for physical assault, which suggests that the young are sexually assaulted because of their sexual attractiveness rather than because of their vulnerability. We argue that the strong relationship between sexual attractiveness and age reduces opportunities for consensual sex among older inmates. As a result of blocked opportunities for consensual sex, older men are much more likely to commit sexual assault than one would expect, given the general tendency of young men to be more violent. Thus, the age–attractiveness relationship can parsimoniously explain the contrasting age patterns one observes for offenders and victims.