First part: Lot of people who workout barely do any cardio, there's even this belief that cardio will make you lose muscle mass, but unless you're an athlete it's completely ridiculous to worry about that. The people that are in the best all around shape are very often not the ones who look the most fit or that are the strongest. We need fat on our body as an energy reserve, just doing cardio doesn't build enough muscle mass to slow down the effects of aging on it, just building muscle mass without doing cardio means your heart might be the weakest link in your body...
Second part: Not sure, I guess they mean that it takes a while to not feel fine from the damage accumulated from not taking care of yourself and by the time you don't feel fine anymore most of the damage is irreversible... I guess it's true for many things... If you damaged your knees from being overweight for a long time, suddenly losing weight won't make the cartilage reappear for example...