Well, first, it is a locker room. Second, we're all going to age and none of us will look like 20 year old studs when we do. It's called life.
Third, these old guys you refer to have reached a wonderful point in their lives where they don't give a crap what you think about their bodies. Good for them.
Our American society is pretty ignorant when it comes to nudity. We are the ones with the screwed up values. And this has gotten worse since the 70's.
During the 60's and earlier, locker room showers, nudity, swimming nude (single gender) were all the norm. Then the touchy feely 70's came along and suddenly no one had to suffer the embarrassment of group showering (some of this was related to the cost of maintaining and operating the showers) and swimming nude was verboten.
Nudity for all ages should be expected in a locker room; for all ages, not just for pretty boys.
Personally, I prefer to wrap a towel for my walk to/from the shower/locker, but I don't care if you're nude or not or if an old man is nude or not. Get over yourself!