Objective To examine differences in the functional recovery trajectories between younger and older adults with mild–moderate traumatic brain injury (TBI) in the first year postinjury as well as health-related quality of life. Design Observational cohort. Setting Level one trauma centre in the State of Washington. Participants Adults with mild–moderate TBI (N = 34; younger adults, n = 19, and older adults, n = 15). Interventions None. Main Outcome Measures Functional Status Examination (FSE) and health-related quality of life (HRQOL; SF-12v2). Results Older adults consistently showed significantly worse functional performance than younger adults following TBI in the following FSE domains: mobility, ability to travel, home maintenance and overall functional status. For both groups, preinjury physical health was significantly correlated with ability to travel and social integration at 12-month postinjury. Older participants’ preinjury physical and mental health had significant and negative correlation with their functional status. Conclusions Our study provides insights and implications into adults’ specific functional impairments following TBI, and which domains have persistent deficits. Implications for Practice Early intervention and rehabilitation should focus on improving older adults’ physical functioning and mobility. Our study may also inform future research and design of post-TBI interventions for older adults.