Immune checkpoint inhibitors (ICI) are now routinely used in multiple cancers but may induce autoimmune-like side effects known as immune-related adverse events (irAE). Although classical autoimmune diseases have well-known risk factors, including age, gender, and seasonality, the clinical factors that lead to irAEs are not well-defined. To explore these questions, we assessed 455 patients with advanced melanoma treated with ICI at our center and a large pharmacovigilance database (VigiBase). We found that younger age was associated with a similar rate of any irAEs but more frequent severe irAEs and more hospitalizations (OR, 0.97 per year). Paradoxically, however, older patients had more deaths and increased length of stay (LOS) when hospitalized. This was partially due to a distinct toxicity profile: Colitis and hepatitis were more common in younger patients, whereas myocarditis and pneumonitis had an older age distribution both in our center and in VigiBase. This pattern was particularly apparent with combination checkpoint blockade with ipilimumab and nivolumab. We did not find a link between gender or seasonality on development of irAEs in univariate or multivariate analyses, although winter hospitalizations were associated with marginally increased LOS. This study identifies age-specific associations of irAEs.