In 1991 My grandfathers doctor said to my Mum he'd clearly loved to have put 'Old age' on the cert , (Grandpa was 91, and had not been ill) but had to enter another cause also, renal failure was put down as cause, due to old age.
By 1993 when Grandma died ( the widow) the law had been amended and the words 'Old Age' alone was acceptable