Researchers developed a standardized processing pipeline for Garmin step-count data and tested it in 67 older adults (mean age 71.4). Wearable-derived steps significantly predicted 9 of 16 cardiometabolic and fitness outcomes including cardiorespiratory fitness, body composition, and lipid profiles, with participants averaging 5,794 daily steps. Self-reported exercise showed zero significant associations with any health measure. This stark difference highlights a critical blind spot in aging research. Traditional questionnaires systematically underestimate the activity-health relationship, potentially obscuring real benefits of physical activity interventions. The findings suggest decades of epidemiological studies may have undervalued exercise's protective effects in older populations. For practitioners, this reinforces the superiority of objective activity tracking over patient recall when assessing health risks or intervention outcomes. The standardized data pipeline also addresses a major technical barrier preventing broader adoption of wearables in research. However, this preprint awaits peer review, and the relatively small sample limits generalizability. The work represents an incremental but important methodological advance that could reshape how we quantify physical activity's role in healthy aging.