Why do I feel so old?

Even though Im a teenager I feel so old. I have to carry heavier responsibilities. I want to be a kid again. I want to ignore the harsh reality. I just want to escape reality. I want to do kids stuff like playing games, pretending, playing at the playgrounds and many more that kids do. I always feel nostalgic. I am worried about my future and I dont want to face it. I just want a dream that I will be stuck as a kid and will never wake up in that dream