It's immoral if you're a selfish brut and are not giving your old lady the high, hard one because you're always pounding it. Lots of middle-aged guys are like this. They know it's immoral.
On the other hand, if you've got a little energy left over after taking care of the family, or you are out of town and not expected to stand it up at attention like a soldier on command for anyone special, then it's generally not a problem. Just lie back naked and squeeze one off in the hotel room and let the housekeeping staff deal with the fallout. That's what I always do.
Or if you're one of those who don't even have an old lady, of course.