The link above is a GREAT start.
You need to have people skills for recreational groups. Some groups already know what to expect but most don't so they look to you for advice. Safety is obviously of the utmost importance so if there is danger on the field you need to asess the situation and act fast. A lot of people don't even understand why goggles and barrel socks are so important so you need to show authority and make sure players are safe.
bottom line - you're protecting peoples eyeballs so make sure they leave with just as many as they showed up with.
As long as you're old enough to fill out a W2 (tax form) which I believe is age 16.. but I could be wrong, and the field has no age restrictions, then you should be allowed to reff, given there are job openings.