"At 54yrs of age I'm still getting faster."

Me, too, but not much. My first Century ride, Seagull in 2005 (age 50), took 7.5 hours on a course as flat as a table. After a year of serious training, I got that down to 4:58 in 2007 (yes, in pace lines much of the time!), still a personal best for a Century. Since then, I've decided that climbing rides are the thing, so I use rides on Skyline drives as the metrics. At age 58 I'm a touch faster than I was at 52 But, the differences are now at the 3% level.

So, not slowing down yet, but I expect I'll soon reach the point where staying the same will be the main goal....