To analyze missed rib fractures and proper time for evaluation on CT at different ages and to determine factors that favor missed fractures. One hundred patients with rib fractures who underwent CT were classified into three groups according to their age: young, middle-aged, and elderly. CT was performed within 1 to 6 weeks after trauma. The imaging features and temporal changes of rib fractures were analyzed. At the first CT during the initial week, 638 ribs were detected with one or several fractures, overall 838 fractures were confirmed, and 6 were suspected. In the next 2-6 weeks, 47 occult rib fractures were additionally detected. The number of additionally diagnosed fractures was the highest in respectively the 3rd week among younger, 4th week in the middle-aged, and 6th week in the elderly groups. The detection of occult rib fractures was significantly delayed in the middle-aged and elderly groups compared with the young group (p < 0.05). The time to form bony callus was also significantly (p < 0.05) delayed with age, with significantly (p < 0.05) more time needed to form bony callus in the middle-aged (23.8 ± 4.5 days) and elderly (28.48 ± 5.1 days) groups than in the young group (18.0 ± 2.2 days). Most rib fractures can be detected within the first week after trauma. Detection of occult rib fractures will be delayed with increase of age, and repeated CT scanning should be appropriately postponed in patients at different ages. Trabecula, inner and outer plates, costal angle, and cartilage are the primary locations for occult and subtle fractures which should be carefully evaluated. • More rib fractures can be detected on repeated CT scans, especially for subtle and occult rib fractures. • Detection of all rib fractures helps relieve the patient's concerns and determine the degree of personal injury for appropriate evaluation.