Wie alt bist Du? means: how old are you?
You are fast.
Du bist der absolute Hammer! = You are totally awesome!
Bist du = are you (informal, singular)
Du bist so weich = You are so soft
It means "When will you be at home?"
translated it means are you ready
bist du in Ordnung = are you okay
"Du bist bärenstark" means "You are strong like a bear" (literally) or "You are husky". But in colloquial speech the word "bärenstark" can also mean "really awesome". So it depends on the context.
Du bist eine hübsche Frau, du bist süß. = You're a pretty woman, you're sweet.
"Are you with me?" That would be a translation of the question "Bist du bei mir?". The start of the sentence as in the Bach/Stölzel aria "Bist du bei mir, geh' ich mit Freuden" would be better translated as "If you are with me (or: if you're near to me), I go light-hearted (or: with gladness)".
Du bist nett = you're nice, or you're kind.
du bist scharf = you are sharp