Leon and
Onceapilot, '770 had very probably been overstressed beforehand by Rolls Royce (and perhaps RAF pilots) during repeated aerobatics, such as were frequently seen over Hucknall after RR engine trials. One pilot is thought to have looped the aircraft, although barrel rolls and rolls-off-the-top were more normal.
As the first prototype, '770 wasn't as strong as production Vulcans and RR didn't conduct the internal leading edge checks which Avros did after any aerobatic flights.
Neither is it by any means certain that the Syerston accident was caused by the pilot either flying too fast or rolling and pulling - he could have been flying within the planned flight parameters but in an aeroplane which had been severely damaged by others. It was all too easy to find 'pilot error' as the 'obvious' cause in those days.....
On the subject of 'g' tolerance, I know of a chap who's over 60, yet regularly flies to high 'g' limits in fast jet aircraft.... Perhaps old age and treachery does indeed always overcome youth and skill?