If you age backwards then do you end up looking like a baby?

Yep

does your outer only age backwards or all of you? Because if I have to have ED when I look like i'm in my 20's that would be a true hell.

Who doesn't like a high five? Think of all them calories you'd burn from high fiving everyone everyday of your life also all those friends you'll make. High fiving could be your thing. People would learn to love and accept it. It's not that horrible of a situation.