[Paul Atreides]

I am wondering, how old were these planes that were used in the terrorist attacks?

[supercat]

I am wondering, how old were these planes that were used in the terrorist attacks?

Why does it matter? Break the sound barrier in a 757/767 and it will crash, regardless of its age. The stresses on the airframe at mach 1 are far beyond those experienced at 900fps. No matter how well built it may be, a plane which is not designed to survive the sound barrier, won't.