My understanding for the implementation of that rule is it is to avoid new people from coming on with the purpose of recruiting, harassing or advertising via PM. Most of our admins can't see PM and thus, we can't take action if one of the three things i've mentioned above takes place. 20000 XP is needed as it gives the player ample time to get familiar with the rules of the server and also filters out those that aren't there to play but to recruit/advertise/harass as those guys may not be bothered to achieve that amount and head off to another server.
Some admins, however, may set you in advance or before you get 20kXP if you appear to be a good regular by engaging politely with the rest of the players, helping out the admins by evening teams or reporting issues. Ultimately, being a regular on forums can help speed it up too. Purchasing VIP can also help you bypass that rule of 20000XP as you will be receiving an admin level (5,6,7) depending on which one you decide to buy. Discovery of continuous foul play or breaking of rules will result in you being set back to 0 again though.
At the end of the day, we all just want to have fun and ensure the community regulars on our server stay happy so the future of FA is more secure and guaranteed. We take necessary steps to ensure this. I hope you understand my reasoning. I may have missed something out, so a staff member or above may want to clarify what i've said.
Thanks for coming on to the forums to ask