Analysis of 892 adults found that fathers who smoked before age 15 or were overweight during puberty had children with accelerated epigenetic aging across multiple validated clocks, including PCHorvath and PCGrimAge measures. The effect was substantial — daughters showed 1.5-year acceleration from paternal early smoking, while both sons and daughters of formerly overweight fathers showed 2-3 year acceleration in biological age markers. Notably, maternal adolescent exposures showed no such associations, pointing to unique vulnerability during male pubertal development. This finding illuminates a critical but underappreciated pathway linking generational health — paternal lifestyle during the teenage years appears to program offspring aging trajectories through preconception epigenetic mechanisms. The implications are profound for public health messaging, suggesting that adolescent boys' smoking and weight management may influence their future children's longevity potential decades before conception. However, as this medRxiv preprint awaits peer review, these striking intergenerational effects require validation in larger cohorts and mechanistic studies to understand the underlying sperm epigenetic modifications. The research represents an important step toward understanding how parental health choices create lasting biological legacies.