With regard to some our more mature performers not bowing out gracefully - there is a two-pronged reason for this I think -
Firstly the performer is keen to continue to enjoy the unique buzz of live performance which has been the centre of their life for as long as they can remember, and secondly, the audiences want to experience the 'magic' of the original performance, and are prepared to forgive the simple fact that it is never going to be a strong as it once was.
This leads to a combination of artists who still perform, but are by any reasonable measure past their best - and that includes Ms. Paige and Mr McCartney, but also those who are as sharp as they ever were as live performers, and that includes people like the immortal Rolling Stones.