We compared the age structure of three populations of Teleogryllus oceankus that differed with respect to their exposure to parasitization by an acoustically-orienting parasitoid fly, Ormia ochracea. Within two unparasitized populations, females were, on average, younger than males. Female age did not vary across the three populations but males were younger, on average, in the parasitized population. Sexual differences in age structure within populations may arise due to differential risks associated with pair formation. Because we only know of a single parasitized population from which we can sample, we can not be sure that some other ecological difference does not account for the observed variation in age structure across populations. However, the decreased age of males in the parasitized population is at least consistent with the notion of viability selection on males.