Children

I'd say that it's normally a gradual process. For example, they should become responsible for getting to school on time and getting their homework done while they're at secondary school. After that, they should be resonsible for coping with work/college/uni etc. Somewhere after 18 and by the time they're 21, they should be able to cope with most day to day things. In their 20s they should become responsible for their own home, for example

But all of us benefit from advice and support, no matter how old we are, especially if a major event needs dealing with.

That’s a hard one. Depends on so many things. Their circumstances, the lives they lived as children, people they’ve met, experiences etc. A person who feels fulfilled once becoming an adult, would do all these things naturally I would think. Why do you ask? Is there a particular reason?