Jackie Joyner-Kersee, who won Olympic medals well into her thirties when most athletes had retired, understood something subtler than the cheerful platitude of "you're only as old as you feel." She's pointing to how we internalize society's timelines—the moment we accept that certain doors close at certain ages, we've already locked them ourselves. A fifty-year-old contemplating a career change doesn't fail because of wrinkles or slower reflexes; they fail because they've accepted the invisible script that says "people like me don't start over." The power in her observation lies in recognizing that the physical fact of aging is negotiable only through the mental stance we take toward it.