מדרש על מלכים א 2:1

Similarly, concerning King David it is written: Now King David was old (I Kings 1:1). When he drew near to death, it is written about him: Now the days of David drew near that he should die (ibid. 2:1).

And thus do you find with David, that he charged Solomon his son only close to his death, viz. (I Kings 2:1) "And the days of David drew near to die, etc."

And drew near. Our sages maintained that everyone about whom it is written drew near to die failed to attain his father’s age. Drew near is written with regard to David, as it is said: Now the days of David drew near that he should die (I Kings 2:1), and he failed to reach the age of his forebears: Obed, Boaz, and Jesse. Our sages said: The sum of their ages was more than four hundred years, while David lived only seventy years. Hence he did not attain the years of his forebears. Therefore it is written about him: Drew near that he should die (ibid.).