In my head the logic would say that a 14mm aorta has extremely thin walls and should not be able to withstand as much pressure as a normal size?

Not logical: The internal dimension (lumen) of your aorta tells you absolutely nothing about the thickness of the walls. Are the tires on a baby carriage (tiny) more likely to burst than the tires on a 747? I'm not sure what has caused you to become so obsessed with your 14 mm aorta? Do you have a family hx of sudden aortic rupture? What has happened to make you so upset about this?