Good day to you, and greetings to you in the name of the Lord Jesus Christ who is forever blessed.
To get down to business:
First, the thing is if you keep reading the context of the chapter it supports how we are no longer to walk as the rest of the Gentiles walk (Ephesians 4:17). We are told to put off the former conduct (bad behavior) (Ephesians 4:22).
17 "This I say, therefore, and testify in the Lord, that you should no longer walk as the rest of the Gentiles walk, in the futility of their mind,
18 having their understanding darkened, being alienated from the life of God, because of the ignorance that is in them, because of the blindness of their heart;
19 who, being past feeling, have given themselves over to lewdness, to work all uncleanness with greediness.
20 But you have not so learned Christ,
21 if indeed you have heard Him and have been taught by Him, as the truth is in Jesus:
22 that you put off, concerning your former conduct, the old man which grows corrupt according to the deceitful lusts,
23 and be renewed in the spirit of your mind,
24 and that you put on the new man which was created according to God, in true righteousness and holiness." (Ephesians 4:17-24) (NKJV).
We are told to be angry and sin not (Ephesians 4:27).
Let him who stole steal no longer, (Ephesians 4:28). This sounds like overcoming a particular sin to me (Which in this case would be stealing).
One is not really putting off their former conduct if they are still sinning daily or weekly. They would be walking as the Gentiles walk.
Second, Jesus said be ye perfect as the Heavenly Father is perfect. This is in context to DOING certain things like loving your enemies, giving to those who desire to borrow from you, etcetera. The Heavenly Father is perfect not because He believes on the finished work of the cross (Because God needs no Savior) but because God is perfect and holy in His conduct. We are to be as perfect as the Heavenly Father is according to the words of Jesus (of which I cannot see how you believe them in this particular instance with your current belief). 1 Peter 1:16 says, "Be ye holy; for I am holy." God desires us to be holy as He is. Imagine that? But to the carnal mind it sounds impossible. But with God, all things are possible. During the time of the Old Covenant, the Israelite was capable of winning against great odds when their enemies outnumbered them in battle. The carnal minded Israelites throughout history did not think it was possible to win in such scenarios. So it is today. Men today walk by sight and not by faith in what God says.
As for Romans 7:14-24: Again, this is an infamous passage that is used by those who attempt to excuse sin and deny true Sanctification that leads to eventual perfection in this life. The surrounding context (the chapter itself, the previous chapter and the following chapters) does not support the notion that one is a slave to sin as a Christian. Romans 6, Paul says that we are not slaves to sin but we are slaves to righteousness. Romans 7 sets out to talk to those who know the Old Law (i.e. the Laws of Moses) setting the framework that the struggle Paul was having was when he was under the Old Law and not the Laws of Christ. This is obvious when you keep reading in the next chapter when it says in Romans 8:2, "For the law of the Spirit of life in Christ Jesus hath made me free from the law of sin and death." So the Law of the Spirit of Life in Christ Jesus (New Covenant Law) sets us from the Law of Sin and Death (i.e. the Torah or the Old Law). This is why Romans 7:6 says we are to serve in newness of spirit and not in the oldness of the letter. Paul illustrates his struggle in trying to keep the righteous aspect of the Old Law (Romans 13:8-10) (Romans 8:4) in Romans 7:14-24 because he was under the Old Law. This again is evident because Paul asks the question: "who shall deliver me from the body of this death?"
Christians would not ask such a question because they already know the answer to such a question in that it is Jesus. Only the Israelite who is under the Old Law still and who does not know Jesus is their Savior would ask such a question. So your sin and still be saved interpretation on Romans 7:14-24 does not hold water (Not to mention it is immoral because God cannot agree with your sin).
Respectfully, that is incorrect. If one is a mature adult, they are not going to be making the same mistakes they did as a child. Your not mature if you are enslaved to sin. So the next time you slip up into sin, can you really say you are mature? Surely not. It would mean you are a slave to sin and not a slave to righteousness. If a person declares they will always sin (then they are declaring that they are a slave to sin). Jesus says the person who sins is a slave to sin and a slave (slave to sin) will not abide in the house forever (John 8:34-35). We see this truth illustrated in Matthew 13:41-42. In Matthew 13:41-42, the Son of Man (JESUS) will send forth his angels and they will gather out of HIS Kingdom all who do iniquity (sin) and they will be cast into the furnace of fire (i.e. the Lake of Fire). So those in Christ's Kingdom who justify sin or make a defense for sinning will be cast out of Christ's Kingdom at the Judgment.
Again, the argument against being perfect is demolished by looking at the whole counsel of God's Word. As I stated before, Jesus said be ye therefore perfect as your Heavenly Father is perfect. God does not justify sin. So you cannot either. 1 Corinthians 2:16 says we have the mind of Christ. Jesus did not justify sin like many Christians today do. Do you have the mind of Christ? You cannot have the mind of Christ if you justify the idea that you must sin again. The 144,000 are found without fault before the throne of God. This was in context to their holy conduct (See: Revelation 14:1-5). The list goes on and on and you have to duck, dodge, and ignore the whole counsel of God's Word at every turn. I mean, I would pray over these verses and be really sure. Because if you are wrong, you have everything to lose, my friend (By not submitting to God's way of righteousness).