I didn't say it was 'best', I said it was when it was most like itself and unlike anything else. Adulthood - a zenith of identity.
I agree with this idea, but it raises a question or two
We tend to regard genres as organic or biological entities - as a person (growing through the ages of man: infancy, childhood, adolescence etc etc) or as an ecosystem (evolving, mutating, expanding, assimilating, withering)
Does this make sense - seeing social constructions and assemblages as living, quasi-natural systems? It seems irresistible to think of them in those terms but I wonder if there's any reality to it.
But going with that conception of a sound or subculture as a living, growing thing - that leads to the melancholy thought: when a genre achieves adulthood (formative phase completed, influences shaken off) it enters its prime, but that can only ever be a brief moment before the next step, the onset of decline and senescence.
With genres, that doesn't take the form of the musical equivalent of arthritis or Alzheimer's, but genres as they age out do mimic one characteristic of the aging mind, which is inflexibility and an inability to generate fresh perceptions or thoughts.
The character hardens and becomes a confinement.
It happens to genres and individual artists alike - they become predictable. You know what they are going to say before they open their mouths. They repeat the same anecdotes. They have their little catchphrases.
It's that thin line between achieved style and self-parodic mannerism.