Each referee has a rating which tells what level of games they are considered capable of refereeing.  The rating system is as follows:

5	New referee, can only do assistant refereeing
4.5	Can begin to center referee U6/7/8 games
4	Can center U6/7/8 games
3.5	Can center U6/7/8 and begin to try U10 games
3	Can center U10 games and below
2.5	Can center U10 games and below, and begin to try U12 games
2	Can center U12 games and below
1.5	Can center U12 games and below, and begin to try U14 games
1	Can center U14 games and below Can center U16/19 games depending on referee's age
Regarding level 1 referees, please note that the referee must be two years older than the players in order to referee that level game (i.e. to referee U14, the referee must be 15+).

The rating system is updated at the end of each season.  To be promoted to a “.5” level, a referee needs to have shown they are fully competent at their existing level.  To be promoted to a whole number, the referee needs to have done several games at their current .5 level, and to have shown they are capable of working at this level.