Baby Boomers might not consider themselves as growing old but are starting to reach the last quarter of average life spans. This article asks how Boomers prepare for their fourth quarters through physical activity. Three years (1999–2001) of National Health Interview Survey data yielded 96,501 adult respondents. Dependent variables were moderate, vigorous, and strengthening activity. Old boomers (1946–1955) and young boomers (1956–1965) were compared to respondents born before 1926, after 1975, and 10-year cohorts between. SUDAAN multiple logistic regression adjusted for complex sampling structure and multiply imputed income. Age-adjusted, older cohorts showed greater likelihood of activity than younger cohorts, offsetting moderate-activity declines with age until sharp decreases at advanced age: a plateau across Boomer and younger-aged cohorts. Interventions should promote activity at intensities and frequencies to which Boomers are most receptive.