The short answer: only cover up if you want to.
This always bears repeating.
Wear what you want and cover what you want, because you want to, not because someone else says you have to. (Obvious exception for work/school dress codes, but also let’s not pretend those are free of bias.)
You’re not too fat. Your belly is just fine. You’re not too old. Your legs aren’t too long or short; your boobs aren’t too big or small. You are perfect and you can wear what you like. Show off whatever parts you like. Or cover them. Whatever.
Now, not every style will necessarily be available to fit you. That doesn’t mean that your body is wrong or that it’s a sign you shouldn’t wear something. It might mean you have to get creative, but you should still wear what interests you and display whatever parts of your body you want (um…and legally can).
So no, you shouldn’t cover [insert body part here] unless it’s something you want to cover. But think about why you want to cover it. Has the world been telling you your belly is too soft or your thighs are too wide and that’s why you want to cover up? There’s no wrong answer, and it’s your body so you get to decide what to put on it, but it’s always good to think a bit about why we hold certain opinions. Sizeism, like many other isms, is drilled into us from an early age, so what we think is innate may just be the conditioning of a fatphobic society.
It can be liberating to show off something you’ve always been told not to. Sure, they first time you walk down the street in a crop top or short skirt it may feel awkward. But if you keep doing it you’ll discover parts of yourself (not just your belly or thighs) you didn’t know where there.
That doesn’t mean you have to suddenly be ok showing off previously unseen parts of your body. It’s still your decision. But try not to let fat hate dictate what you enjoy wearing.