If I am ever going to solve world hunger, and I've always felt I should at least try, then 2009 is going to be the year. It might not be famine. I might bring peace to the Middle East, or cure a disease, or invent a door that people carrying boxes can open. But whatever my magnum opus turns out to be, it's going to happen this year or not at all. Because, according to Professor Timothy Salthouse of Virginia University, when I turn 23 next year I will already have begun the slow but inexorable process of mental decline.

Salthouse studied 2,000 people over seven years, regularly testing their reasoning, memory and mental alacrity with a series of complex puzzles. In nine of the 12 tests, 22-year-olds came out top. After that, it's downhill all the way.

By 22, Pitt the Younger was in parliament. (Two years later, just as the intellectual downturn was kicking in, he became prime minister.) At the same age, in 1797, William Claiborne became America's youngest congressman. Mozart had already completed all five of his violin concertos and his piano concerto Jeunehomme, described by Alfred Brendel as "one of the greatest wonders of the world". I have just a few months left to catch up with them.

I used to dream of maturing like a fine wine, eventually developing the Wildean wit and encyclopedic knowledge that people always have in films but only Stephen Fry actually has in real life. This notion that as we get older we'll get better is one a lot of people share. But if decline really sets in as early as 23, I should probably get working on my exciting new type of door sooner rather than later.