In brash new music (eg early jazz, early rock), brash new people are at their best. I still prefer Louis Armstrong Hot Five,early Duke Elligton early Stones, early Dylan etc etc.Say 2 years into their careers but not as much as 10. Ignore the first LP, look at the next few. But more reflective music that's going with a longer cultural roll....well like McGrath says, nothing but total decrepitude stops the Carthys and Coppers getting better and better. Have to say though, that the serious, creative innovators virtually always do it early, it's only interpreters that improve after 40.