So, recent work in the UK indicates that "the first age at which there was any marked decline was at 27 in tests of brain speed, reasoning and visual puzzle-solving ability," but that then stays in tact for the next ten years. Alternatively, "abilities based on accumulated knowledge...increased until the age of 60."
I'm curious to see if this research divided people into classes based on education level, or whether or not people participated in ongoing challenging mental activities (e.g. are people who constantly stimulate their brains academically more or less likely to score well on the memory test at each age group, when compared against a those who do not use critical thinking skills on a daily basis?).
Who knows, maybe brain decay is something that, on average, hits us all the same. Or, maybe it depends on gender?