I don't think it is normal but may be it is.
Welcome to te group :-)
I consulted Dr. Google and found the following. It sounds like a discussion with your doc is in order :-)
"Causes, Symptoms and Diagnosis
Many individuals who do not manifest with any nervous system conditions may have MRI findings of mild cerebral atrophy, which is generally caused by the normal events of the aging process.
Although it is not usually a cause for worry, it is however, recommended that those who have mild atrophy should discuss these findings to their doctors, especially in cases where they also experience weakness and memory lapses. Some doctors may advise another MRI scan of the brain after several months to compare the results and evaluate if there is progression of brain atrophy."