It is probably a good idea to be skeptical of links claimed between blood type and measures of degenerative aging. The evidence to date is either nebulous or shows little to no correlation. Where correlations are found the effects are not large, or are not reproduced in other study populations. Nonetheless, here is another paper on this topic:
Researchers claim that people with an 'O' blood type have more grey matter in their brain, which helps to protect against diseases such as Alzheimer's, than those with 'A', 'B' or 'AB' blood types. The researchers made the discovery after analysing the results of 189 Magnetic Resonance Imaging (MRI) scans from healthy volunteers. The researchers calculated the volumes of grey matter within the brain and explored the differences between different blood types. The show that individuals with an 'O' blood type have more grey matter in the posterior proportion of the cerebellum. In comparison, those with 'A', 'B' or 'AB' blood types had smaller grey matter volumes in temporal and limbic regions of the brain, including the left hippocampus, which is one of the earliest part of the brain damaged by Alzheimer's disease.
These findings indicate that smaller volumes of grey matter are associated with non-'O' blood types. As we age a reduction of grey matter volumes is normally seen in the brain, but later in life this grey matter difference between blood types will intensify as a consequence of ageing. "The findings seem to indicate that people who have an 'O' blood type are more protected against the diseases in which volumetric reduction is seen in temporal and mediotemporal regions of the brain like with Alzheimer's disease for instance. However additional tests and further research are required as other biological mechanisms might be involved."