Turns out it's more of an algorithm, just stay active and it'll open up soon enough. What kind of thread do you want to make?
Another user asked me about it too, so I'm taking it up in the help board. I'll let you know what I find out.
Yeah, I think you need a minimum number of regular posts to make a thread, to cut down on spam bots making new threads and such. I don't know the exact number, but I think it's at least 10 posts.