First off, the question is wrong, because it means I have never sinned. Jesus is the only man that could say He was 'without sin', because He had never sinned.
Secondly, the question itself implies that those sinning are somehow justified and not condemned, because others are sinning like them. The flood disproves that self-justifying theory.
Thirdly, even if 'everyone's doing it', the truth that Jesus did not sin and is without sin, condemns all them sinning against God, because man has lived in the flesh on earth without disobeying God.
And finally, the legitimate question is if I am sinning.
No. I am not sinning, nor have I sinned today against my Lord. Tomorrow is another day to endure temptation, if it comes.
Mat 6:34
Take therefore no thought for the morrow: for the morrow shall take thought for the things of itself. Sufficient unto the day is the evil thereof.
And it's the only question that matters, because God's judgment is upon our works we are now doing, not for yesterday that is past, nor for tomorrow that may not come.
God does not remember past unrighteous, when we turn to do His will. Nor does He remember past righteousness, if we turn against His will.
Another legitimate and all important question in like manner, is if we now have sin.
1Jo 3:5
And ye know that he was manifested to take away our sins; and in him is no sin.
No one in Christ Jesus has sin, in whom is no sin. Not because they are covered by their own grace, to not be condemned for sinning, as though they have no sin. But rather because them in Christ Jesus, have repented from their sinning for His sake.
Only those now sinning have lust in their heart to sin by:
Jas 1:13
Let no man say when he is tempted, I am tempted of God: for God cannot be tempted with evil, neither tempteth he any man:
Jas 1:14
But every man is tempted, when he is drawn away of his own lust, and enticed.
How many fall short of the glory of God ?
True. Many, not all.
For all have sinned and continue to fall short of His Glory.
True. All men save one have sinned and made themselves enemies of God. Which is why all men must repent for Jesus' sake, to be saved from sinning against Him.
Act 17:30
And the times of this ignorance God winked at; but now commandeth all men every where to repent:
Mat 1:21
And she shall bring forth a son, and thou shalt call his name JESUS: for he shall save his people from their sins.
1Jo 3:5
And ye know that he was manifested to take away our sins; and in him is no sin.
all will fall short of His glory until the day they die
What happened to only many? Now it's all are sinning and shall still be sinning?
Once again, just because we want to believe everyone else is like us, doesn't mean it's so. And as we've seen, even if everyone on earth is still sinning like you, that only means no one is saved and justified by Jesus Christ.
Not everyone is wilfully sinning unto death:
1Jo 5:16
If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death: I do not say that he shall pray for it.
And even fewer willing sinners guarrantee they do so unto death, by indoctrinating themselves into it. God says in such cases of wilful sinning without repentance, not to even pray for them, since they have set themselves to do so unto the end. It's the same as when the Lord commanded Samuel to stop wasting his time praying for king Saul, since the Lord had already rejected him, by knowing that Saul had already turned away from Him unto death.
That's why certain doctrines are so pernicisouly destructive, because they convince people to not bother repenting of all their sinning, since they have determined they will always continue doing some sins and trespasses.
It's another offshoot of justification by faith alone. They declare they will always be sinning on earth from 'time to time'.