Dame Sheila Hancock looked like she was breezing through old age. She had weathered and even thrived in widowhood, taking on acting roles that would have been demanding for a woman half her age. She has energy, friends, a devoted family, a lovely home. She can still remember her lines. So why, at 88, having sailed past supposedly disturbing milestones – 50, 70, even 80 – without a qualm, does she suddenly feel so furious?