Some people take longer to grow up than others.
The business of being an adult is complicated, and it takes a while to get it right. It could be argued that the majority of grown-up people who feel like they have never achieved whatever the heck it means to be competent at this so-called adulting. Pretty much everyone, even the most mature among us, has one or two things that they struggle with that they kind of assumed they would get the hang of when they were kids.
A big part of learning to become independent in this way starts in childhood. In theory, it is one of the most important jobs that parents have when they choose to have children. They aren’t babies forever, and there comes a point where helplessness stops being mildly annoying and starts to be a real problem.
For various reasons, some have a harder time adjusting to adult life than others, and they will take more time to achieve those basic milestones that they should be capable of. Still, that doesn’t mean that they should be sheltered from reality and allowed to stay in their comfort zone all the time.