It’s not really 30 post, but rather 30 Activity points that you need to reach Jr. Member (since you’ve already got the required Merit). That will take longer than making 30 posts (read FAQ: Everything you need to know about forum 'activity, account ranks and merit )

You can bypass the restriction by acquiring a Copper Membership, but It requires paying to obtain it: https://bitcointalk.org/index.php?topic=2728840.msg27932988#msg27932988