A proper youth stock will also be shorter in the pistol grip portion lessening the reach of the trigger finger to the trigger. A properly fitted youth stocked gun will also have the CG of the gun moved due to the shorter barrel to a point that it helps the swing and makes the gun less muzzle heavy.
Your weight isn't an issue...I weighed a buck-15 at that age. The issue is size...yours vs. the gun. If you are having trouble holding it I'm guessing you are on the short side of 5'6". That comes with the attendant shorter arms and smaller hands. If that is true, a 14"+ length of pull stock is your enemy. If that is true, simply cutting down the stock is not necessarily the answer: I'm on the shy side of 5'4" BTDT.
Since you have about 3 maybe 4 more years to gain any height, how do you stack up against the other men in your family? If you will probably get a couple or four more inches get a full size that you can finish growing into. If you are probably topped out, a youth may very well be your answer.