My parents were the opposite. My mom got very mad when I moved out and she said that children should live with their parents in their 20s or until they got married. Since I really had no plans/thoughts of getting married, I wasn't buying that. She did have some good arguments on finances and how you can be an adult despite living with your family. Although we are of a slightly different culture where you often see multiple generations living in the same household.
I personally don't think it makes you less of an adult to live with your parents. What I think makes you less of an adult is if you live with whoever and don't carry your weight. If you are paying rent, paying for expenses, doing chores, saving money, etc, then how are you more of an adult by living by yourself or someone other than your parents?
I have a relative who lived 'on his own' but was constantly in financial trouble due to his own bad decisions and immaturity. I would consider many people who live at home much more than an adult than him.