Actually, he says, there is so much rubbish talked about age - as if, when you hit certain landmarks, you start to think and act differently. He's getting quite worked up as he talks and it becomes apparent that age itself is the new authority figure to rebel against. "There's a certain wisdom we are supposed to get, and I'm not really convinced that happens. I mean, you're wiser to a degree. But there's a certain archetype - a tried and tested road for artists in their autumn years: more meditative, less concerned with temporal things and more concerned with spiritual things, all that sort of stuff - I was looking forward to that, but it hasn't really arrived."
And I'm still looking at Cave's hair. Is that really his natural colour? He bursts out laughing. "I've been dyeing my hair since I was 16."
What colour would it be? "I hate to think."
For someone who's actually read the whole 200-odd-pages of the biography "Bad Seed" that's just pure birthday gold.