25 y/o with 5+ year study gap — how to apply for Japan on my own?

Hi everyone,
I’m 25 years old and I have a study gap of more than 5 years after completing my 12th grade. In my country, most agencies that process applications for studying or moving to Japan have refused to work with me because of this gap.
So now I’m trying to understand how I can handle the process by myself, but honestly I don’t know where to start. If anyone here has successfully applied to a Japanese language school or moved to Japan without using an agency, I’d really like to know how you did it.

A few specific questions I have:
1. How can I process my documents and apply on my own?
2. Are there any language schools in Japan that are more flexible about long study gaps?
3. I’ve heard that if the study gap is too long and you don’t have strong proof of what you were doing, the embassy might reject the visa. Is that actually true?

Any advice, experiences, or guidance would really help. Thanks!

by RaFih00