So the way to progress is to play with people. And you will get bodied, like absolutely trashed. That's just how it goes when you haven't been playing the game for long. It gets better, don't worry.
I would recommend getting facebook (I know, it's archaic) and finding your local scene's facebook page. If you have trouble finding that, you can post about it on r/SSBM in the general daily thread (I recommend subscribing to this reddit). Playing with people in person is really good and important. I recommend playing against some really good people, as that is important. But when you're literally just starting, playing against people not that good is okay. You can get more out of somewhat close competition, instead of just getting utterly bodied.
But joining your local scene is the biggest single thing you can do to improve. I joined competitive smash when I was your age (five ish years ago), and it can be awkward since at least for me, I didn't have a liscense and stuff like that. And the average age will be older (about five years older, mostly college students). And convincing parents can be difficult. But at least in my experience, people are almost always respectful and understand you're trying to learn the game. The more you stick with it and keep at it, the more friends you will make and the better you will get, ect. Also with convincing parents, if you meet a few people who are really nice and kind and helpful and you introduce these people to your parents, that can go a long way.
In terms of importance, after finding local players, there's other good stuff you can do. Finding a friend to learn along with you is optimal and super fun and just an awesome way to learn Melee. It creates friendly rivalry which can be really good for improving. Also people recommend not playing against CPUs or stuff like that. But when you're literally just starting, it's fine to play against some CPUs to get basic control stuff down. Just know people won't play anything like that and will adapt. Playing through adventure mode can be fun and decent practice when just starting. Just be sure to move on from these most basic steps as quickly as you can.
Netplay is an incredibly useful tool if you have access to it. It's not a replacement for playing with people in real life but it's still really good. You can play friendlies with people or play low ranked players you find (most people on netplay aren't awful though, so it will still be a struggle at first). Ranked can be addicting so watch out for that.
If you have anymore questions during this process, feel free to post them on this thread. I'm sure other people have similar questions.