It's okay to move onto fresh ideas! I started writing a novel when I was 17, and the draft currently has 72,205 words. I put a lot of effort into it, and I really like how I wrote some of the bits... but it just doesn't feel like a good story anymore. I'm uncomfortable with some of the things I portrayed, there were several major plot holes, and a lot of the side characters were irredeemably flat. I'll probably never finish it. But it really helped me sharpen my writing skills, and I've taken that into my current project, along with many of the themes I did like from the novel. I've grown a lot since then, but working on the novel helped me grow.

If you're starting over, you should just make all new characters for the next project so it doesn't feel like the old one. Don't keep the characters or the setting, but keep the dynamics you liked. Recycle the themes you found the most compelling, and spin them with a nuance you didn't have as a teenager. You're more informed as a writer, artist, and person in general since the last time you came up with a story plot. You'll be able to tell this new story better!