I'm not sure that "right" and the implied "wrong" are appropriate.
On one occasion, during a public transport strike, I was given a company car so that I could get to work next day. The proviso was that I had to pick up my boss on the way in. No problem. He was a nice guy. Intelligent, well dressed, interesting, and able to control the office with a light touch. He's the sort of boss I'd wish for all my friends to have. He invited me in for a coffee and I was stunned at the mess. It was everywhere.
There's no right age to stop being messy. Some people are tidy, some are not. If you have a teenager you may be in for a long haul.
If you live alone, own your home, and are not in violation of health and safety ordinances, forever. Who would care? And who would visit you? Living in a dirty and untidy environment can be associated with mental illness and depression and also reflects a lack of self respect, the latter which often manifests itself in extreme laziness. Teens are exempt from these things because they do often go through a period where sloppy is (what they believe to be) the new cool. They learn it isn't either from their parents or on their own.