Incorporating the perspectives of positive psychology, intersectionality, and life course into minority stress theory, this study aimed to examine the relationships between social support, identity affirmation, and psychological well-being among 483 Italian individuals with bisexual orientation, accounting for differences in gender identity (cisgender vs. non-binary) and age groups (young, early, and middle adult). A mediation model was tested in which identity affirmation served as a presumed mediator between social support and psychological well-being. We also examined whether gender identity and age group moderated the hypothesized associations. Multivariate ANOVA and multigroup mediation analyses were conducted. Results showed that (a) cisgender individuals had higher social support and psychological well-being than non-binary individuals, but not identity affirmation, which was higher in the latter group, (b) psychological well-being, but not social support and identity affirmation, differed between groups, with the youngest cohort reporting worse health than their elders, (c) identity affirmation mediated the relationship between social support and psychological well-being, (d) mediation was significant only in binary individuals (compared to cisgender), whereas no age differences were found. Overall, this study highlights the need to consider bisexual individuals as a nonhomogeneous population living multiple life experiences, especially when minority identities intersect.