Sure.

The actual delineations between the Advanced and Casual Subforums are largely artificial because the distinction in the official posted standards is extremely faint and vague. According to the actual forum qualifications, Casual and Advanced subforum members are practically indistinguishable from one another. I have seen Casual subforum regulars who belong in Advanced and write exclusively at an Advanced level, and I have seen Advanced subforum regulars who are so awful they might only be fairly characterized as members of the mythical 'Free' subforum (it is something of a forum Urban Legend in case you were not aware).

In my opinion - and this is just that, so take it however you like - the shift between Casual and Advanced is not one or merit or talent, but of commitment and dedication to a given project. How much time and effort you are willing to spend writing, improving upon your writing, discussing a roleplay with other posters, collaborating, etcetera. That is the distinction I think should exist between the subforums - Casual should be for people for whom roleplay is just another hobby, and not even a primary one at that. Advanced should be for a writer for whom the process is more of a dedicated art and ongoing process.

Do not ask yourself whether you are good enough to write at an Advanced level, because the question is irrelevant due to how the subforums are set up. Ask yourself instead: How important is roleplaying to you personally? How much time and effort are you prepared to invest in it?

If the answer is "A lot," then go for it. Even if you are not wholly confident in your abilities, and even if you are in fact complete trash, simple dedication and practice over time will get you where you need to go - and the Advanced forum is probably the best place to get that experience.