Flying with thoracic aortic aneurysm, is this okay?

Usually, yes. If your aneurysm is stable, and there is no indication for surgery at this time, flying is ok.
Ask your doctor. Flying itself does not increase your risk of rupture -- if your aneurysm is large enough to warrant repair, it may be unsafe to be far from medical attention if a problem develops. Your doctor should be able to help you with this.