Antibody production following vaccination can provide protective immunity to subsequent infection from pathogens such as influenza. However, circumstances where antibody formation is impaired after vaccination, such as in older people, require us to better understand the cellular and molecular mechanisms that underpin successful vaccination in order to improve vaccine design for at risk groups. By studying responses to seasonal influenza vaccination, we show that T follicular helper (Tfh) cell differentiation is impaired in older people. This age-dependent defect was not due to contraction of the TCR repertoire with age, and instead involved the aberrant expression of genes normally repressed by BCL6 in Tfh cells, such as Lamin A. Together, our data suggests that impaired BCL6 function limits Tfh differentiation and restrains humoral responses to immunisation in older people.