The "old man" and the "new man" are terms used exclusively in the writings of the Apostle Paul.

Simply put, the "old man" was your old life or old nature that was full of evil desires and deeds. Your "new man" is your new life that is godlike, created after God, empowered by the Holy Spirit and is righteous and truly holy.

Various translations translate the "old man" as: our old self (NASV), our old sinful selves (NLT), our old life (NCV), the persons we used to be (CEV), our old way of life (TM), our old being (GNT), your old evil desires (LB), our old unrenewed self (AMP), and our old personality (NWT).

God's Word tells us that at the cross God put a death blow to the part of you that used to love to sin. That redemptive act of Jesus put an end to sin's reign in our mortal bodies, freeing us from sin's slavery (Romans 6:6, 11‑13, 17‑18, 22).
The "new man" is translated by these various terms: the new self (NASV), your new nature (NLT), a new person (NCV), a God fashioned life (TM), a new and different person (LB), living a new life (NIRV), the new personality (NWT), and the regenerate self (AMP).

The "old man" is a personification of all that is evil. The "new man" is a personification of all that is righteous and truly holy (Ephesians 4:24).

The basis for godly living is sound doctrine, the Holy Spirit, the "new man," the words of Jesus, and the teaching of the 12 Apostles who were taught directly by Christ. This information constitutes what the Apostle Paul calls the putting on of the "new man," created in righteousness and true holiness (Acts 2:41‑42).

The basis for unsound doctrine is the teaching of false teachers. Its teaching is derived from twisting of the Scriptures and changing that which was intended by the original Apostles. This false teaching allows what Paul calls the "old man" to thrive among the Christian community.

The teaching concerning putting on the "new man" and putting to death the "old man" is found primarily in the teaching of the Apostle Paul. It is the basis for godly living in a believer's life and its foundation rests in the redemptive work of Jesus Christ and the empowerment of the Spirit of holiness that is given to the believer (Romans 8:12‑14).

The Apostle Peter tells us that the Apostle Paul writes some things in his letters to the church that are hard to understand.
The point I am trying to bring out is that people twist the real meaning of the Scripture to something that it does not mean. Changing the meaning of Scripture always leads to disaster and spiritual ruin.

Examples of distorting the Scripture are: let's go on sinning so that God's grace may increase (Romans 6:1), let us do evil that good my result (Romans 3:8), claiming that the resurrection of the dead has already occurred (2 Timothy 2:18), grace allows us to live immoral lives (Jude 1:4) etc. All of these are distortions of Scripture that in some form promotes the works and deeds of the "old man" (the flesh).
Notice this is saying, we must put off our "old man," and we must put on our "new man."

So put off, throw off, give up your old way of life with its characteristics and manifestations of,
And put on the "new man" with the fruit that the Holy Spirit produces in our lives:
The "new man" is a way of thinking and acting that reflects God's own Person. It is the fruit of God's Spirit. A person puts on the "new man" by allowing the Holy Spirit to influence their thoughts, feelings, and actions (Romans 8:13‑14).

I am reminded of the story of the evil King of Israel Ahab and his evil wife Jezebel.
Oh that we might follow the example of Ahab the evil king, to humble ourselves, to turn away from the "old man" and its evil deeds, and walk softly and tenderly before the Lord each day. Why should sin be our ruin?

Abbreviations of Bible Translations
King James Version (KJV), New American Standard Version (NASV), New International Version (NIV), New Living Translation (NLT), New Century Version (NCV), Contemporary English Version (CEV), The Message (TM), Good News Translation (GNT), Revised Standard Version (RSV), The Living Bible (LB), Today's English Version (TEV), God's Word Translation (GW), New International Readers Version (NIVRV), Amplified Bible (AMP), Easy-to-Read Version (ETRV), Bible in Basic English (BIBE), NT in Modern Speech (Weymouth), New King James Version (NKJV), Complete Jewish Bible (CJB), English Standard Version (ESV), Holman Christian Standard Bible (HCSB), New Revised Standard Version (NRSV), New World Translation (NWT).