[mindcrime]

Well what if those decades were your childhood?

That's unfortunate, but luckily a lot of the damage that we do to our bodies can be reversed. No matter where you are, you're almost certainly better off if you start eating right, exercising, etc., today.

As others have said, seek medical advice if you think it's necessary. If your health is so bad that you think you aren't capable of working out and what-not, get a medical professional involved if possible.

And consider that "working out" doesn't necessarily mean going to a gym, wearing weird clothes, doing crazy contortions, lifting weights, etc. I can be as simple as walking 30 minutes around your neighborhood.