ABOUT at the beginning of a sentence is common in conversation.

You can't use 'until' in that context. 'Until' denotes a period of time that starts now and ends at the specified time. So your sentence would mean 'do I have to start doing my homework now and continue doing it until tomorrow', which is not what you mean. You either mean 'do we have to do it by tomorrow' which means that tomorrow you can hand it in finished, or 'do we have to do it tomorrow' which would mean you had all of tomorrow to do it, and could hand it in next morning. I think you mean 'by tomorrow'.

so what is wrong with that sentence? Could you clarify?

yes you can start a sentence with about. But your sentence is incorrect it should be "about the homework, do we have to do it tomorrow?" or "about this homework, don't we have to do it until tomorrow" . You will get disagreements on where to place the "?".

I think use "homework"in place of "it" that is better