From Robert McCrum in Guardian.co.uk:
…The ruthless cut-off of 40 does not address the complex trajectory of creative growth: for every novelist or poet who explodes skywards with a first or second book, there are many who only achieve mastery as they reach the shady side of the slope. The onset of middle age, or the approach of oblivion, is perhaps as sharp a spur to literary effort as the intoxicating self-belief of youth.