Instead of "healthspan," we should be thinking about "Peakspan." How long can you maintain ~90% of your peak physical or cognitive function? According to a new paper, different systems reach their “Peakspan” at very different times. Fluid cognitive abilities like processing speed and working memory peak early, around ages 20–30, while crystallized intelligence doesn’t peak until the late 40s or early 50s and can remain stable into the 70s. Cardiorespiratory fitness peaks from adolescence to the mid-20s and then declines steadily, while muscle strength peaks in early adulthood and falls sharply after 60. Bone density, kidney function, hormone levels, sensory function, immunity, digestion, and reproductive capacity all follow their own trajectories too—some peaking in the 20s, others in the 40s or 50s. In other words, human aging is asynchronous. We don’t simply age “overall,” but instead age system by system.