Really surprised being level headed at 17.The staff are approached by the leaders of the site, I am sure every one had specific reasons for their invitations but at a base level it is an offer made to active, knowledgeable and respectful members of the community who contribute to the site. Having time on your hands is nice, but isn't usually a factor.
The forum needed more staff, I was an enthusiastic, sensible and level headed member (Rob's words) so I was among those picked, even though I had just turned 17. It's just babysitting you lot and it gives me more freedom to write up articles for the subforums I am responsible for as a Moderator. Admins fine tune the background stuff and make sure the forum works as it does. As a team we have members online most of the time to keep it tidy. The majority of our work is actually in the marketplace.