12 years old coolant and 5K miles?

Hoping to hear any guidance or experience others may have on this one. I have a bead on a 12 years old very low mileage (about 5K) Mustang GT 4.6L. It’s some distance from me so I am working from photos and other records. It appears the owner has not changed the coolant since new, despite the six year replacement interval specified in the maintenance schedule. How damaging is this “deferred maintenance” likely to be? Minor concern, change soon as one can? A reliability nightmare that will cause endless problems? Would appreciate any light you folks might shed on this one. I know it’s not a S550 but it’s an all aluminum engine and this forum is much more active than the S197 forum, so hoping to generate some helpful direction. Thanks.

 

Thanks for suggesting this. Appreciate any other input from forum members who have experience or perspectives on low mileage cars with original, overdue coolant inside.