Checked for a date on the tyres and found (20051049), so I guess they were manufactured in 2005. (Didn't know that tyres are supposed to be dated. Will keep that in mind when purchasing replacements.) The ruptured tyre appeared very flexible, with no visible cracks and it seemed to feel the same as it always had on the road. Now hoping that it was a faulty tyre from the start, and that the remaining 3 don't do the same thing. One good thing about the blow-out - at least it happened while it was parked at home and not during a ride.