Pastoral Retirement?

John Newton wrote the following to his friend Rev. William Bull in 1802:

"I am now two days in my seventy-eighth year. My health and strength are remarkable for my age; but I feel some symptoms of declining years. The day of opportunity wears away, and the night is approaching when no man can work. But while the Lord enables me to preach, and the people are attentive and willing to hear me in my poor broken way, I ought to be willing to live to the age of Methusaleh, if I might but promote his glory, and be any way useful to my hearers. I am bought with a price, ergo, I am not my own. I wish to say from my heart, Lord, grant that the short uncertain remnant of my time may not discredit my profession, by pride or any evil tempers; and that when the summons shall come, it shall find me ready and waiting."