The bottom sentence is perfect, but for the first sentence, the present tense form of 'did' is 'do', so it should be "What do you want to be when you grow up?"

The correct way should be "What do you want to be when you grow up" (future) or "what did you want to be as you grew up" (past)

If you're talking to one of your adult friends and talking in the past tense, you can add some words in front of the sentences so it can make a bit more sense. Ex. "When you were a kid, what did you want to be when you grew up?" For the first sentence, I would talk to a child under the age of 18. I would reword it a little. Ex. "What do you want to be when you grow up?"