If you turn 19 during 2005, you are a SENIOR!

Juniors:
if you turn 18 during 2005, you are a junior until 12.31.2005.
If you turn 17 during 2005, you are a junior until 12.31.2006.

Cadets:
If you turn 16 during 2005, you are a cadet until 12.31.2005 and then you become a junior on 1.1.2006.
If you turn 15 during 2005, you are a cadet until 12.31.2006 and then you become a junior on 1.1.2007.

Cubs:
If you turn 14 during 2005, you are a cub until 12.31.2005 and then you become a cadet on 1.1.2006.
If you turn 13 during 2005, you are a cub until 12.31.2006 and then you become a cadet on 1.1.2007.

Bowman:
If you turn 12 during 2005, you are a bowman until 12.31.2005, and then you become a cub on 1.1.2006.
If you turn 11 during 2005, you are a bowman until 12.31.2006, and then you become a cub on 1.1.2007.
If you turn 10 during 2005, you are a bowman until 12.31.2007, and then you become a cub on 1.1.2008.
If you turn  9 during 2005, you are a bowman until 12.31.2008, and then you become a cub on 1.1.2009.

Yeoman:
If you turn  8 during 2005, you are a yeoman until 12.31.2005, and then you become a bowman on 1.1.2006.
If you are  7 or under on 12.31.2005, you are a member of the yeoman division.

 ( courtesy TSAA)

 Division Age calculator here