I have a three years old domain with too many pages which was not a very successful experience. It has only 300 visitors per day. I don't want to keep the content.

As I know domain age has a good effect on SEO.

Now, I want to totally change the content and the structure of the website. The subject is not very different than the old website. It's an online magazine.

Is this OK? or I should use a new domain.

How to handle many possible 404 errors with minimum damage to SEO?