Cerebral blood flow (CBF) increases from rest to ∼60% of peak oxygen uptake (VO_2peak) and thereafter decreases towards baseline due to hyperventilation-induced hypocapnia and subsequent cerebral vasoconstriction. It is unknown what happens to CBF in older adults (OA), who experience a decline in CBF at rest coupled with a blunted ventilatory response during VO_2peak. In 14 OA (71 ± 10 year) and 21 young controls (YA; 23 ± 4 years), we hypothesized that OA would experience less hyperventilation-induced cerebral vasoconstriction and therefore an attenuated reduction in CBF at VO_2peak. Incremental exercise was performed on a cycle ergometer, whilst bilateral middle cerebral artery blood flow velocity (MCA V _mean; transcranial Doppler ultrasound), heart rate (HR; ECG) and end-tidal PCO₂ (P_ETCO₂) were monitored continuously. Blood pressure (BP) was monitored intermittently. From rest to 50% of VO_2peak, despite greater elevations in BP in OA, the change in MCA V _mean was greater in YA compared to OA (28% vs. 15%, respectively; P < 0.0005). In the YA, at intensities >70% of VO_2peak, the hyperventilation-induced declines in both P_ETCO₂ (14 mmHg (YA) vs. 4 mmHg (OA); P < 0.05) and MCA V _mean (−21% (YA) vs. −7% (OA); P < 0.0005) were greater in YA compared to OA. Our findings show (1), from rest-to-mild intensity exercise (50% VO_2peak), elevations in CBF are reduced in OA and (2) age-related declines in hyperventilation during maximal exercise result in less hypocapnic-induced cerebral vasoconstriction.