I have Becker MC, and if I don't exercise regularly I feel the effects of the MC much more. I have had the MC effect just about every muscle.
MC aside, I had a friend who, in high school, was as thin as a rail and would pretty much eat as much as anything he wanted. I used to warn him that it was going to catch up with him someday. Surely enough, by the time he hit 30 he was probably somewhere around 30lbs overweight. There are also things like heart/cardiovascular disease to consider.
You might want to get some books on "eating clean" and give it a try for a month and see if you see any improvement in the way you feel, even if you don't feel bad, you might not feel as good as you could.
Me and my dad both have Thomsen's and he says he always did what you and me do (I'm 17 by the way) and it worked out just the same for him. He says that when you turn 40 it hits the fan and catches up with you a little bit. But considering how he took care of himself in college, I don't think its as severe as it could be. But hey, better safe than sorry right? Might as well be healthy!