Without any more context, I suspect most people would interpret it as meaning (2). I did, and had to think for a few seconds until I saw the ambiguity to which you refer! You could remove the ambiguity by rephrasing in various ways. Here is one:
Your obligation to work begins at age 30.
although if you want to retain the specifically negative aspect of the original, the following would be better:
Your obligation to work does not begin until age 30.
If meaning (1) was actually what was required, then one way of saying that is:
Working until age 30 is not an obligation.