Brotha, if this is that much of a concern to you or is a situation that made you even think twice, you must be living a good, carefree life.
Their are assholes every where so don't let it bother you, this is why I try to train later, when the gym has cleared out a bit. The gym I used most of my life closed recently and I can't find one that's comparable.
The other thing to remember is a lot of people are just f'n dirty, and don't realize that they are disgusting slobs. I work with a guy like this, leaves shit laying all over, is almost 30 and lives with his parents who clean up after him still. The guy didn't realize that it was a problem until we made it clear, he was a little embarrassed and offended at first but he quickly realized it wasn't going to be tolerated. He's a good guy and would help anyone out but he was just use to leaving messes and someone cleaning them. But age is not the problem, there's people of all ages who can't take criticism and don't know how to respond to someone letting them know they did something wrong, especially in a gym, think of how many guys in the gym have self esteem issues, tough guy syndrome, etc. Sorry but there are just as many whack jobs in the gym as their are decent guys.