What does Scripture intend by the use of, “the old man” (Rom. 6:6; Eph. 4:22; Col 3:9)? Is it an entity, such as a person or an angel? Whatever it is, Scripture’s reference to it attributes it as the determining factor of the quality of an individual and as it has been well said, "love does not function according to the quality of its object, but according to its nature." What is it within a person that determines their words, thoughts, feelings and actions? Is it not the nature of an individual? It could not be more correct to assume the “old man” is the original nature of man, which Adam as the progenitor has hereditarily “passed upon all men” (Rom 5:12, 15, 17, 19).
Whether your view is eradication or existential (continued) concerning the Adamic nature, it cannot affect the receiving or retaining of salvation; but this view does affect the believer’s condition concerning the growth within salvation.
During the pre-Cross dispensation, man possessed a single nature which Scripture ascribes as “sinful” (Rom. 5:12; 7:13; 1 John 1:8); and now in the post-Cross dispensation the believer has been given an additional nature or “new man,” which Scripture ascribes as “righteousness and true holiness” (Eph. 4:24). Through the Spirit, in conjunction with the new nature and through the Cross-restraint condition (effected by Christ and administered by the Spirit) of the old nature (Rom. 6:6), the Father “conforms” the regenerate “to the image of His Son” (Rom. 8:29)—“from glory to glory” (2 Cor. 3:18).
Scripture, for its general usage concerning the sinful nature refers to it as “the flesh”; which nature (flesh) is “the carnal mind” and “is not subject to the law of God, neither indeed can be” (Rom. 8:7). This is that nature which the Holy Spirit opposes within the believer, inasmuch that “the flesh lusts against the Spirit, and the Spirit against the flesh; and these are contrary to one another, so that you do not do the things that you wish” (Gal. 5:17 NKJV). It is also depicted as a dichotomy of natures (old and new man) in Romans Seven, where the new nature is represented as the new “I” (vs. 17, 20), “the inward man” (v. 22) and “the mind” (v. 25); and the old nature represented as “carnal “(v. 14), “flesh” (vs. 18, 25), “evil” (vs. 19, 21).
Finally, the new nature is also depicted as “His (Christ) seed” (1 John 3:9), which complies with Colossians 3:10: “and have put on the new man who is renewed in knowledge according to the image of Him (Christ) who created him (it—new nature).” It is the one “born again” (believer) in his new nature that cannot sin, but still does sin in his old nature (Rom. 7:25). The one “born again” cannot refer to Christ because He did not require regeneration—being the Regenerator—through the Spirit. Neither can it refer to the "seed," which is of Christ's nature and is the product of being born again.
It has been well said, “the lost need saved and the saved needs delivered”; delivered from the bondage of not knowing and thus, not appropriating the freedom available to the believer; which appropriation can be established in walking “circumspectly” (of self, Satan and society), “not as fools but as wise, redeeming the time, because the days are evil” (Eph. 5:15, 16).