What are some possible reasons for accelerated brain aging, moderate cerebral atrophy greater than age?

If there is a history of familial Alzheimer's disease, with a genetic cause, this may explain atrophy at the age of 56. However, it would indeed be prudent to have a neurological consultation and undergo a full evaluation.

A CT or MRI that is revealing for cerebral atrophy that is greater than expected for a person's age requires a complete neurological evaluation with attention to the person's clinical symptoms, family history and physical/neurological exam. Additional studies including blood work, PET scan, EEG, and neuropsychological testing will be done at the discretion of the neurologist to obtain a diagnosis