How long can you live with untreated aneurysm?

Depends on size: With increasing size there is more risk of rupture which is frequently catastrophic.

Difficult to say: The risk of complications from aortic aneurysm is variable. Many factors, including size, symptoms, BP management, ..... All influence the likelihood of having a complication. For aneurysms greater than 6 cm in diameter, rupture occurrs at 3.7% per year, rupture or dissection at 6.9% per year, death at 11.8%, and death, rupture, or dissection at 15.6% per year. This risk increases with size.