Many factors can influence perceptions of successful aging (SA), including social isolation and poor physical health. We hypothesized that social support attenuates the negative effect of plasma D-dimer, a correlate of HIV and aging, on SA. Participants included 230 adults (134 people with HIV; PWH, 96 HIV−), ages 36–65, segregated into age cohorts with up to 5 yearly visits. Multilevel modeling examined longitudinal within-person associations between D-dimer, social support, and SA. Social support moderated the relationship between D-dimer and SA and was significant among PWH and older individuals (ages 56–65), but not HIV− or younger cohorts. This association was significant only at extreme levels of social support, with significant decreases in social support potentiating the negative impact of D-dimer on SA and significant increases in social support facilitating increased SA. Despite declining health, high social support may improve SA in PWH and older adults, and low support may be especially problematic for older adults.