[_h_o_d_]

Cognitively, people do slow down after 21 or so. It is likely not to be a linear process, but I'm sure a quick google of research will find this. It is not, as suggested by the other comment, spurious feeling, but a well-known cognitive fact about humans. And experience in eal things doens't help with random tests, expecially if you're 20 more years away from your CS finals.

Whether this translates into a perceptible disadvantage in code tests is less likely to have been tested, but it is given what we know, and given other arguments above, quite possible and indeed likely.

[neeleshs]

At least one study suggests that unlike athletic abilities that do peak at around 20, fluid intelligence is more complex and may peak all the way up to 50 years. http://m.pss.sagepub.com/content/26/4/433