devonianflyer and camelspyyder are spot on about overall proportions and weight.
Overall butt to knee length (measured in the sitting position from the point where your back touches the seat to the tip of your kneecap) and weight are the show stoppers on the medical for a pax flight in a Hawk. Too long in length and you will smash you knees on the instrument panel if you have to eject and your weight in flying kit has to fall within the limits that can be set on the seat's Pitch Control Unit which adjusts the thrust line of the seat's rocket motor through the seat (and your) center of mass. Can't remember what the limits were but I was around 15 stone and 6 foot when I (very much just) passed the medical to do a trip out of Valley in late 93 (Having a 36 inch waist and a Wraf sized backside didn't help). The guy who set the ride up for me tried to get a ride himself only to be overweight for the seat and failed the medical.
