I’m also in my 60’s and play Horde several times a week, but rarely have time for 1-50 runs (8 re-ups). I don’t feel like my reflexes have slowed, but I’ve always had great hand-eye coordination. Was at a store recently, had walked in front of my cart in a busy aisle, and quickly flipped the cart around to go back the other way. Only problem was that I had filled the “baby seat” part of the cart so full that 2 items flew out of the cart, about a foot apart from each other. Without thinking I reached around the cart and caught both items, one with each hand, just before they hit the ground. I quickly looked around, hoping that someone saw it. But no, sadly, I only impressed myself.
https://www.justpark.com/creative/reaction-time-test/ has a reflex test for PC users. Not sure how valid it is, but I tried it 30+ times and routinely scored between 24-32 years old according to it. Also tried it on my iPhone and scored even younger (eliminates the time it takes the mouse to “click”).