The purpose of this study was to compare the effects of different frequencies and intensities of Tai Chi practice on blood pressure, cognitive function, stress levels, and physical fitness parameters in older adults. A randomized controlled trial with parallel groups was conducted over 16 weeks to evaluate two Tai Chi interventions (3×50 min/week vs. 5×30 min/week) in older adults (n = 46). Outcomes included blood pressure, cognitive function (MoCA), perceived stress (PSS), flexibility (Chair Sit and Reach, Back Scratch), strength (handgrip, arm curl, chair stand), agility (8-Foot Up-and-Go), and functional capacity (Six-Minute Walk Test). Post-intervention, TC5d showed significantly better performance than the control group in arm curl (p = 0.017), chair stand (p = 0.001), handgrip strength (p = 0.004), and 8-foot up-and-go (p = 0.041). TC3d performed significantly better than the control group in the 6-minute walk test (p = 0.013). MoCA scores were significantly higher in both TC3d (p = 0.004) and TC5d (p = 0.008) compared to the control group. PSS scores were significantly lower in TC3d (p = 0.004) and TC5d (p < 0.001) compared to the control group. This study suggests that both Tai Chi interventions improve cognitive function and reduce stress in older adults. The TC5d group showed greater benefits in strength, agility, and flexibility, while the TC3d group improved functional capacity. These results suggest that a higher-frequency Tai Chi regimen (5×30 min/week) is more effective for improving physical fitness and mental health in older adults.