look at it another way - virtually every jazz soloist who left something of real worth and excellence did it before he or she was 35ish. (Hawk and Body & Soul one of the few exceptions, Duke in 1940 another, albeith revived by Strayhorn.) After their 'best' work there were gradual or sometimes catastrophically fast fallings-off. I think Artie Shaw sensed this and stopped forthwith. Benny kept the balls in the air for a long time, rewarming old coals and playing 'Airmail Special' right up to the end..