Increasing difficulty balancing in the dark: ive found over the past year or so im having more difficulty keeping my balance while walking in the dark. not so much that i fall, but theres a noticeable difference. what might cause this?

At age 21, a progressive neurologic symptom would not be attributable to "age". Such an occurrence merits a visit to one's doctor and ultimately to a neurologist for a careful neurologic consultation.

Not feasible to pinpoint etiology but some possible problems to be evaluated include the status of retinal rods to see in the dark, proprioceptive issues in the spinal cord, potential demyelinating disorders, vitamin deficiencies, thyroid issues, etc. This should be thoroughly assessed by an experienced neurologist.