Objectives To determine the age-specific clinical presentations and incidence of adverse outcomes among patients with COVID-19 in Jiangsu, China. Design and setting This is a retrospective, multi-center cohort study performed at twenty-four hospitals in Jiangsu, China. Participants From January 10 to March 15, 2020, 625 patients with COVID-19 were involved. Results Of the 625 patients (median age, 46 years; 329 [52.6%] males), 37 (5.9%) were children (18 years or less), 261 (40%) young adults (19-44 years), 248 (39.7%) middle-aged adults (45-64 years), and 79 (12.6%) elderly (65 years or more). The incidence of hypertension, coronary heart disease, chronic obstructive pulmonary disease, and diabetes comorbidities increased with age (trend test, P < .0001, P = 0.0003, P < .0001, and P < .0001 respectively). Fever, cough, and shortness of breath occurred more commonly among older patients, especially the elderly, compared to children (Chi-square test, P = 0.0008, 0.0146, and 0.0282, respectively). The quadrant score and pulmonary opacity score increased with age (trend test, both P < .0001). Older patients had significantly more abnormal values in many laboratory parameters than younger patients. Elderly patients contributed the highest proportion of severe or critically-ill cases (33.0%, Chi-square test P < 0.001), intensive care unit (ICU) (35.4%, Chi-square test P < 0.001), and respiratory failure (31.6%, Chi-square test P = 0.0266), and longest hospital stay (21 days, ANOVA-test P < 0.001). Conclusions Elderly (≥65) patients with COVID-19 had the highest risk of severe or critical illness, intensive care use, respiratory failure, and the longest hospital stay, which may be due partly to that they had higher incidence of comorbidities and poor immune responses to COVID-19.