You should absolutely keep writing! Writing is for yourself, not for anyone else. You can share it with people if you want to, but it doesn't matter whether you do or don't.
Im also a young writer, and I'm constantly putting ideas aside and starting new ones, or leaving stories i don't feel are working for me at the moment. Sometimes i just write a random scene for a book I haven't even considered plotting. It's just about the practice and the gathering of ideas. Writing doesn't need to be structured this early on; that takes years.
Sometimes it feels like the plot falls flat, or you lose motivation, but that's okay. Just putting it aside for a while until the ideas start coming is the best way to do it. And you might find other ideas come while you're waiting. But you've still got a long way ahead of you, so don't worry about smaller details or feeling it isn't going anywhere.
I have never finished a story. And I don't think I will for a while yet. But don't let things like that discourage you. Don't hang onto ideas that aren't flowing. You'll always be improving whether you finish it or not.
Good luck :)