When is it time to move beyond beginner level?

Something I tell my students all the time! 

Don't be afraid to use up your art supplies. When you've completely gone through your first set of paints and brushes, you will have practiced painting enough to move on to more advanced work. If you're not using up your supplies, then you're just not painting enough. You will never graduate from the level of Beginner if you never use up your materials.  

Sometimes my students are frustrated that they haven't attained artistic genius after one workshop, or after taking one semester of instruction. I have to remind them, that if they are still using the first set of student grade materials that they've ever bought, then they are still students. Use up those paints! When you've painted so much that you need to replenish all your paints at least once, you can move on to intermediate.