My Topic Is, How Old should a Christian Live to Be? '... 
 
In Genesis 6 3, God says, “My Spirit shall not always strive with man, for that he also is flesh: yet his days shall be a hundred and twenty years.” 
 
In this verse God set, the minimum number of years that His people should live at 120. This verse could be written, and red like this: “My Spirit shall not always strive with man, for that he also is flesh: yet his days shall be at least a hundred and twenty years.” 
 
Some people, misconstrue this Scripture, to mean that Noah had 120 years to, build the ark, gather the animals, and preach until the flood came. These people say that God was saying that He was going to eradicate mankind from the earth after 120 years, or that God was going to eradicate everybody except Noah and his family in 120 years. They go on to say that God was giving them that much time to repent. Question! If they had repented, is the scripture implying that mankind, might have, continued to live to be close to 900 years old? No! The text says in Genesis 6 13, I will, destroy the earth because the earth is filled with violence, because the sons of God saw the daughters of men were fair; and they took them wives of all which they chose. Verse 5 says, and GOD saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil, continually. Verse 3 says, therefore, his days, shall be, a hundred and twenty years. This is a judgement, not an, if thou repent. Here God is calling man's debt due. See my teaching on Imputation Of Sin. 
 
Regardless of how one might answer the question of, "if they had repented", the premiss that God was saying, that Noah had 120 years to build the ark, and gather the animals, and preach until the flood came, is not what God was saying. 
 
What God was saying, was that he was not going to let man live forever, in his present condition. Yet, he would be allowed to live, at least 120 years. We know this verse is not talking about the maximum number of years a person is promised to live, because, if the 120 years that God was talking about was the maximum, then no one would live beyond the age of 120. However, we have plenty of people in the Bible and elsewhere that have lived beyond 120 years. 
 
Furthermore, Genesis 5 32, says, that Noah was 500 years old when God made this pronouncement. Genesis 7 6, says, that Noah was 600 years old, when the flood came. This means that, Noah built the ark, gathered the animals, and preached for 100 years, not 120 years. The 120 years, has to do with God shortening the lifespan of man, down to a minimum of 120 years. This took place gradually, during the succeeding generations . Previous to this, men were living into their 600's, 700's, 800's, and even 900's. However, during the succeeding generations after Noah, who lived to be 950, men's lives were gradually shortened. Once we get past Abraham, who lived to be 175, and Isaac, who lived to be 180, and Jacob, who lived to be 147, we have no record, in the Bible or elsewhere, of anyone living past the age of 140, with the possible exception of Job, who was given a second life. This means that a person should live to be somewhere between 120 and 140 years of age. 
 
Some Christians say that we are only supposed to live for 70 or 80 years. They use Psalm 90, verse 10, as their “proof text.” 
 
“The days of our years are threescore years and ten; and if by reason of strength they be fourscore years, yet is their strength labor and sorrow; for it is soon cut off, and we fly away.” 
 
A “score” is 20. So “threescore years and ten” would be 70 years, and “fourscore years” would be 80 years. 
 
But to say that Christians can only live for 70 or 80 years is ridiculous, because there are many Christians, as well as many sinners, who live well beyond the age of 80. So this could not be what this Scripture is referring to. 
 
This Scripture, the 90th Psalm, was written by Moses, when the Israelites were wandering in the wilderness for 40 years. They were waiting for all the people who were adults, when they first reached the promised land, and refused to go into the promised land, to die off. These people all died when they were about 70 or 80, because of their numerous sins of not believing God, and their murmuring and complaining during the first year, when they came forth out of Egypt. Their days were passed away in God's wrath, and their years were spent “as a tale that is told”. Their 70 or 80 years were labor and sorrow, and their life was soon cut off and they “flew away”, verses 7 to 10. 
 
We see here that the Israelites who were sentenced to die in the wilderness, only lived about 70 or 80 years. This was their sentence. This does not apply to us, unless we live in sin like they did. Then we may only live to about 70 or 80 years of age, instead of obtaining the promise of a minimum of 120 years. You can't just live any old way you want to and expect to live to be 120, see my teaching on communion. You have to live according to the Word of God in order to receive the promises of God. 
 
Here is a list of some of the people of the Bible, who lived to 120 years of age and beyond, starting from the time of Abraham. 
 
Here is their Name,          Age,           and   Reference.

Sarah -       lived to 127.      - Genesis 23 1. 
Abraham - lived to 175.      - Genesis 25 7. 
Ishmael -   lived to 137.       - Genesis 25 17. 
Isaac -        lived to 180.       - Genesis 35 28. 
Jacob -       lived to 147.       - Genesis 47 28. 
Levi -          lived to 137.        - Exodus 6 16. 
Kohath -    lived to 133.         - Exodus 6 18. 
Amram -    lived to 137.         - Exodus 6 20. 
Aaron -      lived to 123.        - Numbers 33 39. 
Moses -      lived to 120.         - Deuteronomy 34 7. 
Jehoiada -  lived to 130.           2nd Chronicles 24 15. 
Job  -         140 + 2nd life.      -  Job 42 16

Praise God for the reading and hearing of his word! Amen.