While I don't qualify as a "young'un" these days, my mental/emotional/psychological state regarding body image and its relationship to diet and exercise was severely deranged when I was.
Granted, I did work out and I thought that I was eating "right" (the classic chicken sandwich at McDonalds = healthy fallacy), but it was for all the wrong reasons (approval seeking, low self esteem, etc.)
However, my current perspective on diet and exercise is shaped by having had plenty of context throughout my life. I have arguably done the most unhealthy things possible to my body and am now on the complete opposite end of the spectrum (unless we find out that animal fat does in fact cause heart disease and diabetes, then I'm f'd).
This does not preclude others from possessing much higher levels of maturity and awareness that I did, however.
If you are 16 and have a healthy desire to be healthful with regards to your diet and exercise choices, then more power to you!
I was firmly anti-establishment as an adolescent, but I think that its better to focus that natural rebelliousness towards the dietary conventions rather than the legal/ethical ones!