Across plant and animal species, juveniles are generally more susceptible to infectious pathogens than adults. A growing body of research has explored how age-specific resistance evolves and why juvenile susceptibility is maintained in host populations. From the less well-studied pathogen’s perspective, juvenile susceptibility means that most pathogens infect juvenile hosts more readily than adult hosts. In the present study, we investigated whether this pattern of age-specific infectivity varied across pathogen genotypes within a fungal pathogen species (Microbotryum lychnidis-dioicae) infecting a plant host (Silene latifolia). We inoculated four host genotypes with each of five pathogen genotypes at two different host ages (seedling and adult) and scored the proportion infected for each host genotype*pathogen genotype combination. The data set contains the total number of plants scored and the number that were infected for each GxG combination.  We also recorded the sex of each individual disease plant, and this information is also included in the data set.   We found significant interactions between pathogen genotype and host age, indicating variation in age-specific infectivity, and suggesting that this important epidemiological trait can evolve in response to selection. Furthermore, we found that significant pathogen × host genotype interactions determine infection risk for juvenile hosts and vegetative adults, whereas infection risk for reproductive adults is primarily determined by the main effects of pathogen and host genotypes. This suggests that specific immunological interactions may be the main determinants of resistance for juveniles and nonreproductive adults. In contrast, more general resistance mechanisms, such as physical barriers, may be the primary resistance mechanisms in reproductive adults.