A large Danish study comparing two groups of nonagenarians born 10 years apart has found that not only were people born in 1915 nearly a third (32%) more likely to reach the age of 95 than those in the 1905 cohort, but members of the group born in 1915 performed significantly better on tests of cognitive ability and activities of daily living. Additionally, significantly more members of the later cohort scored maximally on the MMSE (23% vs 13% of the earlier cohort). All this even though the later cohort were on average two years older than the first cohort when tested (94-5 vs 92-3 years)
The difference doesn’t appear to be due to education (educational achievement was slightly higher in the 1915 cohort, but only in women, who had overall very low educational attainment in both groups). It’s suggested that factors such as better diet and general living conditions, improved health care, and greater intellectual stimulation have helped the younger cohort improve their cognitive functioning.
 . Physical and cognitive functioning of people older than 90 years: a comparison of two Danish cohorts born 10 years apart. The Lancet [Internet]. 2013 ;382(9903):1507 - 1513. Available from: http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(13)60777-1/abstract