Nearly all Age Group races in Triathlon are Non-Drafting. It is against the rules to travel behind an athlete. Depending on the races governing body, the distance to which you must adhere to is below.
The Draft Zone is always rectangular. It measures from the front of the front riders wheel. As long as you are first in position you may say here but if you find yourself within the draft zone then you must pull back or make a definite effort to ride through. You get 20 seconds to make a ride through effort before you are liable for a penalty.
ITU Long Distance Races: 3mt wide x 12mt long
ITU Standard Distance and below: 3mt wide x 10mt long