Young architects blunder into the unsure world of designing a smart little cafe here, a one-year-wonder shop there ...

An architect friend celebrated his 50th birthday this week. A charming chap and a fine architect, he has, despite the frustrations of his profession, managed to stay looking forever 35. Whether this is through the enviable ability to sleep through client crises or a secret shareholding in Grecian 2000, none of his friends can agree. But, I liked very much the comment from one of his oldest friends that our host is really only 35 and just pretending to be 50.

Why would he do this? Because everyone knows that most architects do their best work in their fifties and sixties. By passing himself off as older he can attract major clients, and by the time he really is 50 he will be able to enjoy a second 20-year stint at the top of his tree.

I still think its the Grecian 2000. Even so, the idea of the age at which architects reach their prime is an interesting one. In a society obsessed with youth, architecture is a frustratingly slow business. While it is possible for 25-year-olds in the US to design a skyscraper, the truth is that they are employed to style the facades, lift-lobby and split-pediment at the top, but not the main structure, which is nearly always the work of a firm of "executive" architects who do most of the work for the none of the credit.

Of course there are architect prodigies such as Sir Edwin Lutyens, who was designing his first raffish and beautifully built country house at the tender age of 19. But for every Lutyens there are several thousand Gradgrinds and many a would-be star designing the occasional kitchen extension in the more distant outreaches of Nuneaton and Leamington Spa.

Architecture takes more than a lifetime to master, as Lutyens and Le Corbusier, two of this century's greatest architects, knew well. As young men, both designed radical buildings (in very different styles), but neither ever stopped developing. Corb's finest work dates from the Forties and Fifties (his fifties and sixties), and Lutyens (although this is arguable) from the Twenties and Thirties (he was born in 1869).

Quite why an architect has to hurry when young is a puzzle. Better to learn one's craft and learn it well than rush into the fray encouraged, unwisely, to believe that youthful energy will triumph over skill and experience. Better, too, perhaps, to have the chance to work on the design and construction of a major building by a talented and experienced architect than blunder into the unsure world of designing a smart little cafe here, a one-year-wonder shop there.

At the beginning of this week I went to Duxford to visit the nearly completed American air force museum, designed by Foster & Partners. For the past five years the day-to-day work on this magnificent concrete hangar (a structural tour de force) has been in the hands of a young architect in Sir Norman's office. What he learnt is something that no number of fashionable art galleries, cafes or kitchen extensions could have begun to teach him. He has worked with some of the country's best architects, engineers, contractors, curators and conservationists (in the company of a Grumman Avenger, U2 "spyplane", Flying Fortress, Superfortress, Stratofortress ...) and that is an apprenticeship worth having. When he hits his forties, he will be well in his stride. If, though, he is tempted to fly the nest, he should dab on the Grecian 2000, throw a 50th birthday party and look to grand commissions