This supplement on ageing contains a number of useful articles on brain ageing. See:
Abbott A: Cognition: The brain’s decline. Nature 492: S4-S5 (Dec 2012); doi:10.1038/492S4a .
Stranahan AM and Mattson MP: Science and society: Recruiting adaptive cellular stress responses for successful brain ageing. Nature Reviews Neuroscience 13: 209-216 (March 2012); doi:10.1038/nrn3151 .