Understanding how aging impacts the function of memory CD4 T cells is critical for designing effective vaccines. Our studies show that immunological memory generated during youth functions well into old age, whereas that generated later in life functions poorly. This is the result of declines in the function of naive CD4 T cells from aged individuals and contributes to reduced efficacy of vaccines in the elderly. To begin to identify the cause of this defect, we examined the function of memory T cells generated from bone marrow precursor cells (BMPC) from young or aged mice in young hosts. In two different models, memory cells derived from young and aged BMPC exhibit good ex vivo and in vivo function. Importantly, memory CD4 T cells generated from aged BMPC exhibit potent cognate helper function for humoral responses, which are critical for effective immunization. These results indicate that there are no apparent age-related intrinsic defects in BMPC with regards to generation of functional memory T cells.