Adult vaccination appears to fundamentally rewire aging immune systems beyond simple pathogen protection, triggering "trained immunity" that reprograms innate immune cells for broader defensive capabilities. Analysis of five major vaccine platforms in older populations reveals unexpected cardiovascular and mortality benefits extending far beyond their target infections, suggesting vaccines function as immune system trainers rather than merely disease preventers. This immunofitness concept represents a paradigm shift from viewing aging immunity as inevitably declining toward seeing it as trainable through strategic interventions. The evidence base spans influenza, RSV, pneumococcal, COVID-19, and zoster vaccines, each demonstrating heterologous protection against unrelated health threats. Precision vaccinology emerges as the next frontier, promising individualized schedules based on immune age rather than chronological age, alongside frailty and comorbidity profiles. For health-conscious adults approaching middle age, this research validates vaccination as active immune optimization rather than passive protection. The clinical implications are substantial: routine vaccination schedules could serve as foundational anti-aging interventions. However, the field still lacks standardized immunofitness biomarkers and long-term studies tracking immune resilience over decades. This represents early but compelling evidence that strategic immunization deserves consideration alongside diet and exercise as core longevity practices.