I smoke just about every day and I'm in great shape. I lift and do cardio. Now, I'm sure if I didn't smoke I would be in a little better shape, but I don't play any sports, therefore I choose marijuana over having a little extra edge.
I'm 25, have been smoking regularly for close to 4 years and I'm in better shape now than I was when I started smoking. Yeah, there are negative consequences to be had, but that comes with a lot of things. You have to pick and choose your poison, just make sure your poison is da bomb digity.