Background The mean age of actively treated subarachnoid hemorrhage (SAH) patients is increasing. We aimed to compare outcomes and prognostic factors between older and younger SAH patients. Methods A retrospective single-center analysis of aneurysmal SAH patients admitted to a neuro-ICU during 2014–2019. We defined older patients as ≥70 years and younger patients as <70 years. For every older patient, we identified three younger patients with the same World Federation of Neurological Surgeons (WFNS) grade. We only included patients receiving active aneurysm treatment. Favorable functional outcome, defined as a Glasgow Outcome Scale (GOS) of 4–5 at 12 months, was our primary outcome. We used logistic regression to compare prognostic factors between the groups. Results Ninety-five (85%) of 112 older patients and 317 (94%) of 336 younger patients received aneurysm treatment. Of the younger patients, 91% with a good-grade SAH (WFNS I-III) had a favorable outcome compared to 52% in the older good-grade SAH group. In poor-grade patients (WFNS IV-V), favorable outcome was seen in 51% of younger patients, compared to 24% of older patients. Acute hydrocephalus and intracerebral hemorrhage were associated with unfavorable outcome in the younger (OR 4.7, 95% CI 2.6–8.4, and OR 3.7, 95% CI 2.1–6.4), but not in the older patients (OR 1.8, 95% CI 0.8–4.2, and OR 1.3, 95% CI 0.5–3.1, respectively). Conclusions In actively treated SAH patients, age was a major determinant of outcome. Factors reflecting increases in intracranial pressure associated with outcome only among younger patients.