I do not believe this blowout was caused by age of the tire.
I believe it was a manufacturing defect(undercure). Have seen
this a few times in my long tire-industry career, but don't
remember one that lasted what, 8, 9, 10 years? A covered spare
is good indefinitely.
IMHO age, to a great degree just a marketing gimmick, has been made a scapegoat for many, many other problems with tires over the last few years.
I would take it to a qualified tire dealer and have them give me
their opinion.
40 years in the tire industry; saw it all and done most of it.