Transitions

I'm sometimes startled by depictions of 'elderly' characters in novels and short stories.  Not so much by what the author has to say about them, but who it's said about. In the example that sparked these thoughts,  the 'elderly' woman was all of fifty five.  What happens, I think, is that the author projects herself forward to some age barely imaginable to the young and weaves a character from a bundle of notions about what that age might be like.
Where do our notions about aging come from?  As a young adult, I remember reading an article about changing fashions that included speculations about what the well dressed woman would be wearing as she stepped across the threshold of the twenty first century.  It occurred to me then that I'd be fifty seven years old at the turn of the century and no longer interested in the minutiae of clothes and hairstyles. 
Who knew?  Fashions haven't changed nearly as much as the author predicted, and I'm still trying to lose 10 pounds and shopping for hair color. 
There's seems to be a persistence of vision at work, an afterimage that lingers long after the observed phenomenon has faded.  At the turn of the last century, fifty seven was old.  That notion has been slow to change.  Personally, I have a long history of being younger than sixty.  Growing old gracefully is trickier than I used to think.  Apologies to any woman I silently judged for clothing or make-up that hadn't kept up with her years!