The demand for total knee arthroplasty (TKA) continues to grow exponentially, and this has been attributed to a higher prevalence of osteoarthritis and excellent procedural success. In particular, with increasing life expectancies and obesity rates, surgeons are seeing patients with a wider age range. Therefore, we assessed the effects of patient age on: (1) range of motion (ROM); (2) pain and function; (3) physical and mental status; and (4) activity levels following TKA. We assessed 278 TKA patients (108 men, 170 women), with subdivision into three age-specific groups: < 55, 55 to 74, and 75 years or older. ROM was assessed and functional outcomes were evaluated using the Knee Society scoring (KSS) system, the short form-36 (SF-36), and the lower extremity activity scale (LEAS). The patients were assessed preoperatively and postoperatively at 6 weeks, 3 months, 12 months, and then yearly thereafter until 7 years. All cohorts demonstrated improvements in ROM, with no significant differences between the age groups. For KSS objective, there were no significant differences between groups after 6-week follow-up, though in pain and motion, the 75 years and older had the highest mean score at final follow-up (97 points). In KSS function, the < 55 years group had highest scores at 2 (90 vs. 87 vs. 75 points) and 5-year follow-up (96 vs. 88 vs. 72 points). For SF-36 and LEAS, the 75 year and older cohorts had the lowest mean scores at various time points. In the mental component, those < 55 years had the lowest scores postoperatively. It is important to understand the effect of age on post-TKA outcomes, particularly as the cohort of these patients continues to grow. Our results demonstrate that comprehensive preoperative discussions and management are needed, particularly in those patients at either end of the age spectrum (< 55 or ≥ 75 years).