I don't think there is a clear answer to your question as everyone advances at their own speed. A "beginner" pattern generally works with straight cuts - possibly fewer pieces, and uses simple strip-piecing techniques. Intermediate can have more pieces, smaller pieces, more involved piecing layouts. Advanced takes it up another notch or two. As you already noticed, even in each category there are levels, and a confident beginner is a good place to be.
If the intermediate patterns look easy to you, then why not try them. My personal recommendation: Make a test block. That will tell you if you can or if there is more to the pattern than initially anticipated. Likewise if a beginner pattern seems hard. Read all the way through the pattern. Often the key is in the layout and cutting directions. It only LOOKS difficult but really isn't.
Sounds like you are enjoying the process and are growing as a quilter. Congratulations!
I was a little over-confident in my beginnings and made a Lone Star quilt way too early. Well, I should say that I started a Lone Star quilt and after 25 years it is still in the box. So I know what you are talking about.