I can think of several solutions:
1. Ignore Newbies when sorting on "Last post" date. This way, Newbies can't bump threads anymore.
This is a good idea but I think that you should bump it up to Jr. Members as well.
Yeah this is what I was thinking too.
When it comes to collect merit the bots will die.
The copper membership can have the privilege to bump a thread, also only Copper members can start an Ann thread /and members above Jr. of course/.