What everyone else said. If it makes you feel better I have a 13.2hh pony that is ridden hard by me (5'8" 135 lbs) and a couple of my friends (5'10" 160) (5'6" 120), and (5'4" 140lbs). When I say hard I'm talking about long trail rides walk, trot, canter, and gallop. When she progresses to jumping I'll be her rider. I will also be teaching her games.
Lily has given me no indication she has any trouble carrying any of us and has plenty of energy and spunk under saddle. Unbalanced riders are more of a problem than heavy/long riders.