Using data from the first national probability sample of Black, White, and Latinx sexual minority people in the United States, we examined whether and how sexual identity development timing and pacing differs across demographic subgroups at the intersections of cohort, sex, sexual identity, and race/ethnicity. Among a sample of 1,491 participants aged 18-60 from 3 distinct birth cohorts, we measured participants' ages of "sexual identity development milestones," including first same-sex attraction, first self-realization of a sexual minority identity, first same-sex sexual behavior, first disclosure to a straight friend, and first disclosure to a family member. Participants from more recent cohorts reported earlier and accelerated pacing of milestones relative to those from older cohorts. Subgroups defined by sex and sexual identity varied in milestone timing and pacing, with gay males reporting an earlier onset of some milestones than other subgroups. Those who used newer identity labels (e.g., pansexual, queer) reported younger ages of milestones relative to bisexual participants but similar ages to lesbian and gay participants. Black and Latinx participants reported some milestones at younger ages than White participants. Race-stratified models testing groups at the intersection of cohort, sex, and sexual identity revealed subgroup differences in ages of first disclosure to family, as well as differences in the time between self-realization, same-sex sexual behavior, and disclosure to a straight friend. The results suggest substantial variation in the developmental timing and pacing of milestones across social identities and the need to further examine how milestone timing is related to identity, stress, and health.