Late-life physiological and clinical impairments are associated with age of first exposure (AFE) to tackle football. There is a dearth of literature describing how AFE may influence physiological outcomes in current high school football athletes. Cerebrovascular reactivity (CVR) measures the cerebral blood flow response to variations in carbon dioxide partial pressures. Understanding how AFE affects cerebrovascular function in high school athletes may offer insight into potential long-term deficits following cumulative head impact exposure. PURPOSE: To investigate how the age at which high school football athletes began playing tackle football influences baseline CVR. METHODS: High school football athletes [n=29; age=15.8 ± 1.1 yrs; height=175.8 ± 8.1cm; mass=75.1 ± 12.6kg] self-reported AFE (median AFE=13 years old, range=5-15). Transcranial Doppler (TCD) ultrasound was used to assess middle cerebral artery velocity (MCAv) prior to beginning the competitive season. Baseline MCAv was collected for 2 minutes. Changes in MCAv were measured in response to 5 breath-holding trials (20s breath-hold/40s rest) and 5 hyperventilation trials (20s hyperventilation/40s rest). We employed separate mixed effects models with quadratic mean structures to assess group differences in MCAv response to breath-holding and hyperventilation tasks. RESULTS: The AFE significantly predicted CVR during breath-holding (F_1,1709=5.27, p=0.02) and hyperventilation (F_1,1709=4.08, p=0.04). One-year increases in AFE were associated with a 0.69% reduction in average CVR response during breath-holding and a 0.58% increase in average CVR during hyperventilation. CONCLUSIONS: Though AFE is associated with CVR in high school football players, the underlying mechanisms driving the observed results are unclear. The effect of cumulative head impact exposure at the high school level is understudied despite long-term neurophysiological deficits reported in retired professional football players. Studying neurophysiological responses in young football players may provide important insights into addressing cerebrovascular function and other late-life physiological health in athletes.