Anybody notice the metric that was used? Auction prices? That is a measure of what two rich men will pay for something, but is that a measure of "peak creativity?"
Here, we pursue photography. At what point do we say we've peaked? The obvious tail-end point is when we no longer can photograph. I've noticed that a number of photographers have stopped after having vision problems. Others just keep going, and there are a few blind photographers. One guy uses a meter modified for Braille (I asked him). So if a photographer can't use the camera, or direct its use, then that's another end point for photography. Quite a bit of great photography happens by sheer chance, like Adams' "Moonrise." Some photographers embrace the "snapshot" ethic, so it's impossible to tell if there ever is a peak, just a drop-off in output.
When did Vivian Maier peak? She's probably closest to the average photographer around here. Going around, quietly and privately exposing film, and then ratting it away. We know that at some point she was too old to go out and photograph. That's the tail end of her productivity. But where's the peak? How about Gary Winogrand? Or Eggleston?
There's really two peaks for a photographer: creativity and productivity. When someone stops exposing film and making prints, then their productivity is ended. The other peak is the creative cycle, but that's a bit different. People fall into ruts, and sometimes do what they've done before because that's what they're "known for." Jerry Uelsmann said in an interview, "What am I supposed to do now, street photography?" The real peak of creativity is when you don't know what comes next! If every print you see is something else, jumping here and jumping there, no direction, whatever idea zips through the mind, then there's no peak. That's where exhibitors go wrong, when they ask a photographer to have a direction. At that point, the photographer is asked to go and be in a rut. The proper exhibition should actually keep the viewers on their mental toes.