To understand the epidemiological variation in bacteremia characteristics among differently aged populations, adults with community-onset bacteremia during a 6-year period were studied in a retrospective cohort. A total of 2,349 bacteremic patients were stratified into four age categories: young adults (18 to 44 years old; 196 patients; 8.3%), adults (45 to 64 years old; 707 patients; 30.1%), the elderly (65 to 84 years old; 1,098 patients; 46.7%), and the oldest old ( 85 years old; 348 patients; 14.8%). Age-related trends in critical illness (a Pitt bacteremia score of ≥4) at bacteremia onset, antibiotic-resistant pathogens (extended-spectrum β-lactamase ESBL-producing , species, and EKP; methicillin-resistant MRSA; and levofloxacin nonsusceptible EKP), inappropriate empirical antibiotic therapy (EAT), and 4-week mortality rate were observed. Using a multivariate regression model, critical illness at bacteremia onset (adjusted odds ratio AOR, 9.03; < 0.001) and inappropriate EAT (AOR, 2.67; < 0.001) were the two leading predictors of 4-week mortality. Moreover, ESBL-producing EKP (AOR, 12.94; < 0.001), MRSA (AOR, 8.66; < 0.001), and levofloxacin-nonsusceptible EKP (AOR, 4.27; < 0.001) were linked to inappropriate EAT. In conclusion, among adults with community onset bacteremia, significant positive age-related trends were noted in antibiotic-resistant pathogens and bacteremia severity, which were related to the increasing incidence of inappropriate EAT and 4-week mortality with age. Thus, different empirical antimicrobial regimens should be considered for distinct age groups.