I had the same feelings well into adulthood. I owned a house, had a job, and was married. Legally, I was in every way an adult. I even kind of acted like it, but in my mind, which had accumulated a lot of experience and knowledge, I still thought and felt like I was 18 or 19 years old. I assumed it would always be like that, but eventually, I did start feeling mature, except without the deep wisdom that was supposed to come with it. I'm not sure if that comes later or if it was just a delusion.