A non-invasive device to measure the dynamics of cerebrospinal fluid (CSF) is highly desirable because CSF facilitates the cleaning of neurotoxic wastes in the brain. A better understanding of CSF dynamics helps promote healthy aging in older adults and to treat patients with neurological diseases. This study employed a multi-color optical method to quantify prefrontal CSF dynamics in two groups: (1) older adults with (n = 16) and without (n = 27) Alzheimer's disease and (2) young adults (n = 26) before and after prefrontal light stimulation. The results revealed that the coupling strengths between cerebral blood volume (CBV) and CSF were age-dependent and significantly higher in AD patients than in healthy controls. Prefrontal light stimulation significantly enhanced CBV-CSF coupling, suggesting improved CSF drainage. This study underscores the multi-color optical strategy as a unique tool for monitoring the interaction between CBV and CSF, as well as metabolic functions in the human brain, while demonstrating the therapeutic potential of brain light stimulation in treating neurodegenerative diseases involving CSF drainage dysfunction.