Other than eyesight degraded a bit on my mid 40s but then they got stable, so I got glasses instead of squinting around. But I can still pass the driving license test (just last year) without glasses, but I need reading glasses or I really have to squint a lot to check messages in my phone without glasses.
For example I can still read a 22 inch monitor set at 1920x1080 at 2 feet distance if I squint enough, but forget about dinner menus without enough light on a restaurant, but with glasses I'm just fine.
Memory is fine, actually my wife and kids always rely on me to tell them where they left stuff, because for some reason I have not only a good abstract memory but also a goo visual one (despite the eyesight). But being a programmer and having to remember projects I worked many years ago is kind of been my life so I guess I get enough refresh cycles to keep my mind sharp.
Motor control is fine as well but I work making video games so I guess I have more training than the norm, at least as on reflexes and muscle memory goes.
As for hearing, well I can really perceive high frequency noises more and more, to the point that I start hauling before my dogs do, kidding on that one, they know someone is coming even if there are people walking down our street all the time, they know when someone is actually coming to our house at least 20 feet before they reach the front of our house (busy Chicago street).
I hate sleeping, I like to do things all the time, if i'm working in something that is interesting I can stay up 2 or 3 days in a row, or with very few sleep like just two hours a night, I've always been able to do that.
I don't go out often but when I do I'll stay until 4am or more if I was allowed to. No problems breaking in the dance floor or singing karaoke and drinking anyone under the table, but I noticed my hangovers last almost one day instead of a few hours. Must be the liver is not working full time and letting more alcohol in my system. But I just need to drink water and take a couple of hours nap and I'm as good as new.
So, not everyone on their 50s are falling apart.