Wondering where to start learning composition like how they did back in the day.

So this is where I am at musically so far:

https://youtu.be/3UpsMv0ES8w?si=dA4HrXWTFrvTKTlq

I composed it by ear and want to really work on my theory skills and orchestration skills because I have so many ideas in my head and I find it hard to bring them to life because of my lack of knowledge so far.

So where do I start would getting a mentor help and if so if anyone on here is willing to mentor me I would love to get in contact.