This is actually more common than you think. Age groups 40-55 are often more competitive than others. This is the age when people suddenly realize they are aging and start training like maniacs. When I run road races, my overall ranking (among men) is always better than my age-group ranking.
Not uncommon, I'm 52 and still beat most of the men who are literally half my age. I even outright win a race once in a while if I'm not on the west coast (much more competitive, I've found). Granted, there's a bit of innate talent and hard training involved.
Frankly, I don't give it a lot of thought, I just run like I always have. It's not until someone else points it out that I'm like "hmm, I guess that isn't too bad for an 'old guy'".
As a sibling commenter pointed out, 50-ish is when the kids move out and you've finally got a little money and vacation time, as well as time to train. Time for that $7000 Colnago race bike you've always wanted, eh?
I swim (since I was 13, that is > 37 years). I also don't train like a maniac any more but simply try to improve my style and keep my fitness. But I hardly meet anyone in the pool half my age who has the slightest chance to keep up. This is not meant as boasting at all. The good non-professional athletes seem to be > 40 these days.
Is that a sign that we don't have good trainers? Or do others only start to work out after the doctor starts to pale while looking at the blood analysis?