The purpose was to characterize gas exchange kinetics following the on-transient of exercise in men aged 30–80 yr. Forty-six men completed square wave exercise tests from loadless cycling to subventilatory threshold (VET) work rates with gas exchange measured breath-by-breath. Signal averaged data were fit with a monoexponential equation to derive time constants (T) for gas exchange and ventilation (V2, τVCO2, τVE) and heart rate (τHR). There was a significant slowing of ventilation and gas exchange kinetics across age with linear regression yielding an increase of 0.67 s·yr−1for τVO, (39 s in young to 61 s in old), 0.57 s-yr−1for τVCO2, and 0.65 s-yr−1for τV2, whereas τHR (44 to 41 s) was not-changed significantly. The-slowed VO2kinetics with age may reflect limitations in muscle blood flow or in control of the rate of oxidative metabolism. The less marked slowing of τVCO2compared with τVO2across age may reflect reduced CO2storage capacity with loss of muscle tissue. The τVE, change across age was similar to that for τVCO2(τVE/τVCO2unchanged). The present study demonstrated marked age-related slowing of gas exchange dynamics at exercise onset.