Little is known about how alcohol treatment rates vary across age or years since onset of an alcohol use disorder (AUD). We examined past-year treatment prevalence and associations across these important time metrics. Method Data on 22,278 adults ages 18–50 were from the National Epidemiologic Survey on Alcohol and Related Conditions-III (2012–2013). We examined the age-varying prevalence of alcohol treatment and associations of past-year AUD severity, MDD status, and DUD status with treatment. Additionally, for individuals with a lifetime AUD (N = 7089), we examined associations of severity, MDD, and DUD across years since AUD onset. Results Individuals with Moderate/Severe past-year AUD had significantly higher treatment rates at nearly all ages, compared to those with Mild or no AUD. For those with Moderate/Severe AUD, treatment rates were highest during late adolescence and middle adulthood and lowest during early adulthood. Mental health comorbidities were positively associated with treatment at certain age ranges in mid-adulthood. Among individuals with a lifetime AUD, those with Moderate/Severe past-year AUD had significantly higher past-year treatment rates across all years since onset. MDD and DUD were both positively associated with treatment at nearly all years since AUD onset. Conclusions Alcohol treatment rates varied notably by age and, to a lesser extent, by years since AUD onset. Greater AUD severity was consistently associated with higher rates of treatment, whereas Mild AUD had a much weaker relationship. MDD and DUD showed similar patterns of positive association with treatment. Our results highlight important subgroups where unmet treatment needs are highest.