You will go to Undergraduate Pilot Training (UPT) for a year just like everybody else before ever setting foot on a big jet. You'll also go to Combat Survival School and have some "Unpleasant" experiences. No amount of civilian experience makes you special enough to skip that. Airline Pilots with thousands of hours have washed out in the past. You are going to train in the T-6A, a tandem-seat aircraft with a Martin-Baker Ejection Seat, an aircraft also used as a "Combat Aircraft" by other countries. So yes, your sitting height matters.