I don't know exactly by what you mean by "too old". My grandfather (one of two) broke one of his hips when he was about 90 something, and the NHS couldn't (or wouldn't) operate on him because they deemed it too risky to his health, so maybe that was the reason in your aunt's case. I guess to a private company, business is business...they just want paying. But no, the NHS most definitely does not discriminate on the grounds of intellectual. Hawking wasn't even famous when his condition manifested...it was because of the NHS that he was able to pursue his academic career. If he had an insurance company, the premiums would have been immense, as he was not expected to live long...he and his family would have had to made the emotional decision over whether it was 'worth' even doing so - if indeed they had been able to pay at all.