Reduced age-specific mortality and increased muscle strength and walking speed of current older adults may have altered the relationships between these factors as more people may be above the reserve capacity threshold. We compared the cross-sectional associations between muscle strength and walking speed, and the associations of muscle strength and walking speed with five-year mortality between two population-based cohorts of 75- and 80-year-old people born 28 years apart. Maximal isometric grip and knee extension strength and walking speed were measured in 2017–2018 (n = 726). Mortality was ascertained from registers. The associations were compared with data of same-aged people studied in 1989–1990 with identical protocols (n = 500). The knee extension strength-walking speed relationship showed plateauing at higher strength levels among the later-born men, whereas the earlier-born men and women of both cohorts with lower strength levels were on the linear part of the curve. In the later-born women with lower five-year mortality rate (1.16 vs. 5.88 per 100 person-years), the association between grip strength and mortality was markedly different from the earlier cohort (HR 1.13 [95% CI 0.47–2.70] vs. 0.57 [0.37–0.86]). For knee extension strength and walking speed, the mortality hazards were similar between the cohorts, although statistically non-significant in the later-born women. In men, the later-born cohort showed similar associations as observed in the earlier-born cohort despite having lower mortality rate (2.93 vs. 6.44). Current older adults have more functional reserve that will likely help them to maintain walking ability for longer while also contributing to better survival.