Memory declines early in normal aging, worsening in dementia. Glutamatergic neurons, abundant in the hippocampus, play a pivotal role in synaptic plasticity underlying formation of associations. We have previously demonstrated with 1H fMRS, significant modulation of hippocampal glutamate during encoding of object-location associations. We observed that the timing of modulation differentiated proficiency in acquiring the associations. Because age-related hippocampal atrophy may be accompanied by glutamatergic dysfunction, age-differences in task-related levels of hippocampal glutamate may provide a marker of age-related memory deficits. Here, we identified age-differences in hippocampal glutamate modulation during associative memory encoding, which may underlie age-related associative memory deficits.