Age-related olfactory decline in humans is well-documented, yet the underlying peripheral neural mechanisms remain poorly understood. We investigated age-related olfactory decline across psychophysical, nasal mucosal, and central neural levels in 73 healthy adults across the lifespan. Participants underwent Sniffin' Sticks testing and simultaneous recordings of mucosal electro-olfactograms (EOG) and cerebral chemosensory event-related potentials (CERP) in response to olfactory and trigeminal stimulation. Older adults exhibited significantly lower psychophysical olfactory scores, prolonged CERP P2 latencies, and reduced spectral power across theta, delta, and beta bands at peripheral (EOG) and cerebral (Fz, Cz, and Pz) sites. These findings demonstrate a systemic decline of olfactory function. Although the olfactory mucosa remains functionally active, diminished neural recruitment and oscillatory power, coupled with slower central processing, characterize olfactory aging. These objective electrophysiological markers provide a comprehensive profile of sensory decline in the aging population.