Verse 2. - And he (i.e. Isaac) said, Behold now, I am old, and know not the day of my death. Isaac had manifestly become apprehensive of the near approach of dissolution. His failing sight, and probably the recollection that Ishmael, his half-brother, had died at 137 (if that was Isaac's age at this time; wide supra), occasioned the suspicion that his own end could not be remote, though he lived forty-three or sixty-three years longer, according to the calculation adopted, expiring at the ripe age of 180 (vide Genesis 30:28).

27:1-5 The promises of the Messiah, and of the land of Canaan, had come down to Isaac. Isaac being now about 135 years of age, and his sons about 75, and not duly considering the Divine word concerning his two sons, that the elder should serve the younger, resolved to put all the honour and power that were in the promise, upon Esau his eldest son. We are very apt to take measures rather from our own reason than from Divine revelation, and thereby often miss our way.And he said, behold, now I am old,.... See Gill on Genesis 27:1,

I know not the day of my death; how soon it will be; everyone knows he must die, but the day and hour he knows not, neither young nor old; and though young men may promise themselves many days and years, an old man cannot, but must or should live in the constant expectation of death.