My last sedan went from 25+mpg to barely 19mpg (24% reduction) over the 16 years I had it. Thats the same curve. Almost every machine gets ****ier as it ages.
I'm not sure why you keep posting in this thread, what are you trying to accomplish?
I’m on almost the same curve on the Highlander I have now. Averaging like 19 MPG over the last 2000 miles. Used to get 25 minimum.