Apologies that you didn't get a reply. For some reason, it doesn't seem to send me notifications, either.
Anyway, you are on the right track! The requirements for getting to the classifieds is "at least 10 positive selling feedback, 4 months of active Arena membership, and be at least 16 years old."
I counted through your feedback and it looks like you have 5 selling/trading feedback. Need just 5 more and you're good to go.