How long is too long for writing a book?

Hi! First off, let me tell you that I am an enormous fan of yours and I grew up reading the Alice books, They’re fantastic! I’m 17 years old and all my life I wanted to be an author. Right now I’m working on 3 books at the same time so I don’t get burned out. I’ve been working on one of the books for almost 3 years! I thought I would be done with it by now but I kept getting writer’s block, life got busy, and at 15 I felt the story and some of the topics were too mature and too I guess big for me at the time so I decided to take a break from it for a while to get a little wiser so I knew what I was talking about because it’s a coming of age/romance book. I started writing it again but I feel a little embarrassed or ashamed that I’ve been working on it this long. Is it normal to work on a story this long? should I feel embarassed? Have you ever worked on a book this long?

I have now been working on the novel I’m currently writing for three and a half years, and I’m not done yet.