when I gain a few extra pounds because of my bad habits, I feel tired, even my family tells me I look older.
At least they are comfortable enough to tell you! :D
but everyone wants slim bodies even if they deny it.
I agree. I don't think I have ever met an obese person who doesn't look at slim people with a pang of envy.
But luckily I have never had a hard time losing weight, my big problem is to maintain a stable weight.
Not sure how old you are - but it can change fast ;D