Objective Major depressive disorder (MDD) is prevalent across the lifespan, but relatively little is known about how age of illness onset impacts the cognitive and affective presentation of MDD. Method We explore depressive symptoms and cognition in 70 adults (30–89 years old) with MDD. Participants were divided into three groups on the basis of age of MDD onset: early (<30 years), midlife (30–49.9 years), and late (>50 years). Symptoms were assessed using the Hamilton Depression Rating Scale; principal component analysis was used to create symptom component scores. Cognitive functions were measured. Results The late‐onset group were significantly older than the early‐onset and midlife‐onset groups. Analysis controlled for age and hemoglobin A1c levels, as some participants had diabetes. The late‐onset group demonstrated greater weight loss and gastrointestinal symptoms compared with the early‐onset group. Suicidal thoughts and sleep disturbance were higher in both the early‐onset and late‐onset groups compared with the midlife‐onset group. Correlations between symptom components and cognitive domains varied by age‐of‐onset group. Discussion This preliminary analysis demonstrates cognitive and affective profiles that are both unique to age of onset and common across MDD. Symptom profiles may assist in identifying factors influencing depression and enhance the clinical evaluation and care of individuals struggling with the effects of depression across the lifespan. Copyright © 2013 John Wiley & Sons, Ltd.