Researchers thought AD was an age-related

 In the past, researchers thought AD was an age-related disorder. However, there's been little research on whether it affects children as well. "We did have a small study from 2002 where they were using older people in nursing homes," said Schaeffer of Vanderbilt University, which involved comparing blood samples between six elderly patients and eight younger healthy volunteers over 10 years. In that work, scientists looked at DNA methylation patterns along with clinical features such as changes to cortisol levels during cognitive performance tests. The idea is that memory impairments should be caused by abnormal protein activity rather than altered neuronal pathways when cells are being activated - or silenced. 

However now scientists are beginning a review of the evidence supporting this notion and suggesting that there may actually BE "aging" symptoms like dementia among young adults regardless if these can be explained by Alzheimer's disease or other mental illnesses.   Here at Brain Age, we have covered many articles on aging here over several years which clearly indicate brain structure (brain size) does NOT change with increasing age;