[Scienz]

At 29 I've also become somewhat paranoid about age-related cognitive decline. From what little I've looked into it, to the extent you go by the fluid and crystallized intelligence dichotomy, fluid tends to peak at around 25 and crystallized peaks somewhere in the 35-55 range (I've heard multiple numbers from different sources), with major decline beginning around 65. Brain mass also peaks around 25 and loses around 2 grams per year thereafter. The intelligence loss seems to be exponential with age - you'll drop a lot faster between 60 and 70 than you will between 30 and 40. The different peaks for fluid versus crystallized probably affect life outcomes differently depending on lifestyle and profession, e.g. the saying I used to hear from my physics professors that "If you haven't done anything by 30, you never will," or the Primer quote, "What they do with engineers when they turn 40? They take them out back and shoot 'em." On the other hand fields requiring vast recall of domain knowledge like law or medicine probably favor the older crowd that have had decades more time to accumulate, even if they lack the high-level abstract problem solving stuff required more in e.g. physics or math.

Some relevant links on all that: http://www.highiqpro.com/wp-content/uploads/2012/03/cognitiv... http://www.brainhealthhacks.com/wp-content/uploads/2011/01/f... http://qph.is.quoracdn.net/main-qimg-fd832e64253819688a4eaaa...

There's also work on reversing cognitive decline with stem cell therapies: http://www.impactaging.com/papers/v4/n3/full/100446.html