The Pilot Elders were a group in Pilot society. They were responsible for determining whether a member of their species was worthy to pilot a Leviathan. Their assessment of Moya's Pilot was that he was not yet being worthy of such a task. The use of the term "not yet" suggests that, after their initial assessment, they would be willing to reassess Pilots at a later date and reconsider whether they were ready.
It is uncertain what relationship, if any, the Elders had with the Peacekeepers. In at least one case, the Peacekeepers bypassed the Elders to get a new Pilot for a Leviathan ("The Way We Weren't"). It is unclear if the Elders would ever provide Pilots to the Peacekeepers given they enslave Leviathans and Pilots with them.