Leagues usually represent the Governing Body that is controlling the game. They should not reference the age level.
Leagues are a way of separating different Game Codes for organizational purposes. Leagues are the top of the organizational chain. Each league will contain multiple Game Codes. If you only have 1 league, you can simply turn OFF leagues altogether so you don't need to worry about them. This can be done in your System Settings by turning off Feature #11.
Usually, if you're going to use leagues it is because you have different pay structures within the same game level (code). For example, if you schedule Varsity games for 2 different leagues that have different pay rates, or you just want to organize the games separately - this would be a good use of leagues.
Leagues combined with Game Codes control your Official Positions. Positions control your officials' fees and how they're scheduled. This can be a crucial building block to getting your system initially setup to your meet your needs. Feel free to Contact Us