Is there an age where you decide to just 'let it go'?
Not talking suicide. But, I mean more like an age where you know you won't be dating anybody and that you don't care if you let some of your health slide. Get a little chubby, drink some beers that you never did before, smoke like you never did before when you spent years avoiding the stuff when you were younger.
Stuff like that. I think I might get into smoking when I'm more into my 40s or something. I don't care, life would've long pass me by then, it isn't like I'm going to be a successful individual at 55 or something.
I fear bad health, not cause what other sees, but cause how it will affect my quality of life. I also fear pain.
I never feared getting chubby. It was never an obstacle to social interactions. I say eat what you want, don't overdo it. If your doctor tells you to stop, then follow their recommendations.
I don't think it's ever a great idea to engage in self destructing behaviour, such as smoking, no matter your age. Avoid messing up your body, and the chances for a happier life goes up.