stress hormones [glucocorticoids] & brain aging…….

"Elevated glucocorticoid levels putatively damage specific brain regions, which in turn may accelerate cognitive ageing. 
"In this study, 90 men, aged 73 years....."

"Significant associations between reactive cortisol at 73 and cognitive ageing differences between 11 and 73...."
"These data support the hypothesis that glucocorticoids contribute to cognitive ageing differences from childhood to the early 70s, partly via brain white matter structure."
S.R.Cox, et al
Does white matter structure or hippocampal volume mediate associations between cortisol and cognitive ageing?Original Research 
Psychoneuroendocrinology -- Volume 62 December 2015 -- page 129