It is hard to get into that field. Fiver is a choice, but heavily saturated. Maybe look into songwriting intensives that you can do in person near you (especially if you are in a city). It is a slow start. It is even better if you have a decent portfolio already that you can show people.

At first it's best looking for people in your town or school. At 15 it will be hard to find people with a similar mindset towards music improvement. Join clubs in school, talk to music teachers, join music classes.

While looking for feedback is important, it is equally as important to collaborate with people and critically think about the music you made yourself.

It is hard to make connections online. Try making a music social media (which is difficult to do, you need to make yourself vulnerable to post your music). Maybe find subreddits (which i have trouble doing). Post music on soundcloud and dm people (only a function on laptop).

If you dm me some a little of your music I'd be glad to listen and give you some feedback.

The best way for me has been to find a group of people that also write music. You all help each other and improve with each other. Think of the group Oddfuture, they came up together and now multiple of them are big time artists.

You looking more towards ghostwriting or what?

Here's something to put it in perspective. I'm currently in college. There are many things I wish I would have started when I was 16. At the time I either wasn't confident enough or thought it was too late.

It would be an amazing passion to have. I suggest go 100% for it, don't hold back just because some inner voice is giving you doubt.

Jon Bellion - Blu

I'm not really sure of an exact gateway song, but that was mine.

Most people's is probably All Time Low because that is his most popular (and I don't think it properly portrays the rest of his discography)