I think anyone can enter flow at any point of the drawing process. The reason why it seems like you can only enter it if you're at least intermediate or better is because that's when your inner critic starts to be satisfied enough with what you're drawing that it stops beating you up, but you can get there at a lower level, little kids do it all the time. Flow becomes easier and easier as that voice shuts up. It's taken me a long time to figure it out, but I've found out the thoughts that you should try to promote in your mind to reach flow and the thoughts that are probably keeping you away from it.
Thoughts that help you reach flow:
>Let your arm dance and flow as you draw. Whenever you notice that it's tense, try to relax it
>"Moving my arm feels so good right now, it's like I'm dancing across the page as I draw"
>"I'm playfully noticing angle relationships, checking proportions, and doing other things which are necessary but I'm doing it in a fun and light hearted way, not turning it into a high-stakes, frustrating math problem where I let it stress me and stiffen up my movements"
>"I don't care if what comes out is good or bad. I do this to have fun and I'm having fun creating. It doesn't need to be a certain quality; the quality will come on its own eventually if I just keep drawing a lot."
