It's called professionalism. The players are expected to comport themselves in a certain manner due to the examples set for the profession and younger generations. If you don't agree with this comment, why aren't the players and coaches allowed to smoke in the dugout? They are of legal age. MLB decided that it would be a bad example for younger generations. Is acting this way what you teach your kids or is there amount of respect that should be shown? This isn't just isolated to "guys playing a kid's game and having fun."
I personally, have no problems if he wants to do it but if he doesn't it often enough to tick off the other team, I have no issue with that either.