40 yards is pretty good for someone your age. This is two totally different positions, though. You need to bulk up and gain upper body strength to be an elite lineman. For kicking, you just work on your lower body and practice, practice, practice. Kickers are really important, so I suggest you go with your desire and dedicate yourself fully to kicking. Try to improve your distance and accuracy. Don't worry about your punting - 40 yards is pretty good for now and just practice inside 20 punts.