People will always have an opinion, but you have to live life the way you want to. It's very easy to tell others what to do, but difficult to implement it on yourself.
Psychologically I should say that a person becomes an adult at the point when he produces more than he consumes or earns more than he spends. This may be a the age of eighteen, twenty-five, or thirty-five. Some people remain unproductive and dependent children forever and therefore intellectually and emotionally immature.