In Matthew 24, it says:
42 “Therefore keep watch, because you do not know on what day your
Lord will come. 43 But understand this: If the owner of the house had
known at what time of night the thief was coming, he would have kept
watch and would not have let his house be broken into. 44 So you also
must be ready, because the Son of Man will come at an hour when you do
not expect him.
45 “Who then is the faithful and wise servant, whom the master has put
in charge of the servants in his household to give them their food at
the proper time? 46 It will be good for that servant whose master
finds him doing so when he returns. 47 Truly I tell you, he will put
him in charge of all his possessions.
The Lord will either return while a person is alive, or upon their death. So long as we are able to work for him, we should do so. However, we should also consider that a person who endures hardship - such as old age - with faith and hope is doing God's work. Even from a hospital bed, a person may still be about the Lord's business.
Many Christians believe that the Lord set a limit of 120 years as the maximum lifespan of a human in Genesis, a decree that began gradually to take effect after the flood. If this is true, then you need not worry about living for centuries before you leave this world.
Genesis 6:
6 When human beings began to increase in number on the earth and
daughters were born to them, 2 the sons of God saw that the daughters
of humans were beautiful, and they married any of them they chose. 3
Then the Lord said, “My Spirit will not contend with humans
forever, for they are mortal; their days will be a hundred and
twenty years.”
There are secular accounts of people living beyond 120 years, but all of them also have detractors who claim that the documentation is lacking; e.g. the person's birth certificate was lost in a war or a fire. The Guinness Book of World Records and some other organizations investigate all such claims, and only those with clear documentation are certified. No certified example of a person living over 120 years yet exists. See https://en.wikipedia.org/wiki/List_of_the_verified_oldest_people which has some footnotes about the disputes. This includes Jeanne Calment, the 122 year-old woman, whose daughter disputed her claim.
A commenter asks: "So is simply keeping the Faith a form of fufilling our calling while on earth?"
I do not want to generalize. God requires much of some and little of others. Remember that the wages for all are the same - the one who endured the heat of the day and the worker who joins the crew an hour before the workday ends (See Matthew 20). A personal anecdote shall suffice.
I visited a woman named Janet in her nursing home many years ago. She suffered rheumatoid arthritis, was confined to her bed and endured great pain. She asked our church to send people to pray with her, and when her unbelieving family visited her, she spoke of her faith in God to them. During my visit, I prayed, read scripture and left her a cassette of Christian music.
After I left the facility, I was overcome by tears and wept more bitterly for her than I had ever cried in my life, but a half hour later I was filled with incredible joy, which lasted for a week. Janet died six months later. At the funeral, another of her friends said something with which we all agreed, "When you were with Janet, it was like the Holy Spirit was pouring out of her." That is what keeping the faith meant for Janet, and what it did for me and others. Though she was dying, she did for me - as her work for God - what I had never been able to do for myself. She set me free from over a decade of depression.
