I don't think that's possible, and nor would it be fair! Not all new members post spammy threads, so don't let some new members spoil it for the rest. If I just signed up for LucasForums itching to ask a good question, I wouldn't want to wait until I've been around long enough to start a new thread.
We Moderators are doing our best to cut down on the thread spam from new members, so just chill for now. When this game comes out, these forums will be flooded with new guys with lots of questions. You ain't seen nothin' yet.