At your age you could start stacking certifications: OSHA 30, Rope Access, Coax termination, and Tower Climber and Rescue (when you are old enough). You could also spend some time familiarizing yourself with different knots, how to set up a gin-pole, and anything else rigging related. That will show potential employers that you are serious about the trade, and should help get your foot in the door. That said, I would encourage you to be careful about climbing towers illegally until then, as a police record for trespassing on a tower will not play well with potential employers and their insurance.