You have to be using the forums for over 23 months and two days. Then you send an application into arn asking if you're cool enough to be a senior member. Then he'll ask you to show him some nudes. Just get over 100 posts
You`ll become a senior member once you reach 100 posts. But afaik there`s no real diff in junior and senior members here. Its the same for all the members no matter what the post count is.
Be 60+ years old, be a member for 2 months, and do a funny dance while recording it with a video camera and send the video into arn. Have 100 posts.