Honestly, I believe that age is but a number. Obviously, the older the more experienced, but young adults need to start somewhere. Whether it be an online game, a job in the real world, a forum, etc. I know that some teenagers are more than capable to be a moderator either in-game or on the forums. As long as somebody has a good mindset, can adhere to the values, contribute their time and positive input to the community, and puts out a good vibe to everyone, I don't see why age should matter. I have worked in restaurants for years. I may not be quite the age that you all think is a "mature" adult, but I have grown up fast. Working in a restaurant is a job that is always revolved around human interaction. I, have learned many many things when it comes to dealing with different situations and I feel as if I would be able to handle a job like this even if I am not 25+. It really depends on the person, their people skills, possible experience working with others, and how they can handle situations. Honestly, I think no matter who they choose for staff, they should be monitored as WELL as trained, (or told what is expected of them) and if the can't adhere to this, they be removed from the team.
As far as the fairness aspect goes, I believe whoever is chosen as in-game staff should be allowed to have a seperate "fun" account. That account should be kept totally seperate, and by no means should anyone know the connection. I feel as if staff should also be allowed to relax and enjoy the game like everyone else. Obviously, monitored as well. If they get caught putting items on their play accounts, it should be a warning, and if it happens again, then direct actions should be taken.
Its not all about who is chosen as a staff member, it is also about Administration and how they adhere to their rules and keep a strict eye on their employees to make sure they are adhering to them as well. Think of it as a business. Without a boss, the company would be nothing. They would be all over the place and honestly, would be doing whatever they want. That is how this game works. Without a strong basis, we have nothing.