I don't know about music college. I think it's important to have a music teacher when you're learning an instrument. But I stopped having a teacher after grade 8.
If you want to learn music after that (as opposed to learning an instrument), I think there is only one real way. That is to listen. Let's assume that you can hear everything in a piece of music, because if you can't your ears are probably not good enough and you should find some other trade. Then everything you know, you can pick up by listening to music or discussing it with people.
Read music reviews, because in every music review, somebody is arguing why a piece of music is good or not. See whether you agree. Form your opinions. Follow your own heart, whether you like this or that piece of music. Because only your own heart can tell you what is good or not.
A good music collection can teach you everything you need to know. Beg borrow (Esplanade has a lot of music) or steal (this is the age of the internet I don't have to teach you how to do it).
Songwriting, just keep on writing until you stumble upon something that you are happy with. It will probably take more than 5 years.
There are some things that are worth going to a university for. Like science, engineering and mathematics. The good news is that mathematics and music use very similar parts of the brain, so in a way taking a degree in those things will probably make you better at music.
Don't take a music degree unless you need it for a job.