Age-discordant and earlier sexual debut are risk factors for HIV among men who have sex with men (MSM). Despite differences in the sociopolitical landscape over time, there are no studies sampling participants from the United States that have examined the role of birth cohort in relations between sexual debut characteristics and sexual risk among MSM. We assessed sexual debut patterns and associations with sexual risk-taking in 812 adult MSM stratified by ten-year birth cohorts (i.e., before 1970, 1970-1979, 1980-1989, after 1990). Sexual debut characteristics differed by birth cohort. In multivariate models controlling for birth cohort, both younger age of sexual debut and younger age of anal sex debut were associated with an increased likelihood of condomless sex. Men born in the 1990s had increased odds of engaging in sexual risk regardless of sexual debut characteristics. Sexual risk reduction interventions tailored to the unique needs of young MSM are encouraged.