Its still true for maths though. Especially original groundbreaking work is usually achieved in youth. Good thing is we don't have to worry about it since none of us are smart enough to be the next Ron Perelman whatever tha age.That doesn't contradict it, though; IQ doesn't lower as you grow older because It's measured in comparison with the rest of the people in your age group, but that obviously shows that cognitive ability and speed does decrease as the years goes by...
Though I think it's absurd to say that one's best work can only be achieved when young, considering all the experience in the particular field you might accumulate, or how your mindset on it might change as you age; look at all the middle-aged scientists and mathematicians.
You tend to get more connections and such that might get you on a team that does the groundbreaking work, though; I guess it does apply, but it's not necessarily impossible to do that type of work when older.
Middle aged mathematicians need to prove that it's a coincedence. Terrence Tao is 47 and does work on Prime numbers.
