When I was in my late teens and 20's I raced at Elite level, won a couple, was always in the top 10 for my region/state and did ok Nationally (once). I injured my knees, stopped racing, relocated to the UK, stopped cycling!
I started again at 50, two years ago after moving to Portugal. I've trained with a semi-pro 24yr old for the last 6 months and my fitness now isn't too bad - much better than I imagined it would ever be again. I should lose another 5kg to be really competitive though, I'm carrying too much extra weight. I'm around 4w/kg ftp and over 18w/kg in a sprint, holding 15w/kg for 10s. I've collected over 230 Strava kom's in the last 2 years - in a region where Pro racing with WT Teams is annual and many come here to train, not to mention local Pro's and Elites.
I'm not as fast as I was in my prime, I know that to be true, but I still think that over 50's - and 60's - can make the younger generations suffer when we want to.