I don't think that the age of the craft is coming into question here. We've got B-52s still in operation that are 30+ years old.
FYI, Columbia just finished a 2-year electronic and structural upgrade to it before this launch, if I've read the report correctly.
Having said all of that, I'm sure that they will leave no stones unturned in trying to find the root cause of this disaster. Structural fatigue could have played into it, but there's just too many variables to rule out anything at this time.
May God bless the crew on their final journey into eternity and comfort their families...
