So, why do you think peter is telling people they "have been" born again, in 1Pet?
For you have been born again, not of perishable seed, but of imperishable, through the living and enduring word of God.
is he just being liberal with the past tense?
Let's take a look in 1 Peter 1: 23
being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth for ever.
These are those who are the saints... "
Here is the patience of the saints; here are they that keep the commandments of God and the faith of Jesus" (Revelation 14:12). These brothers and Sisters are from Genesis to present time, that's did righteous in the sight of God and kept the Commandments of God. But Paul went more unto detail about this corruptible seed in 1 Corinthians 15: 49 And as
we have borne the image of the earthy, we
shall also bear the image of the heavenly.
See Paul and Peter understand that that we must be born again to a spirit body or heavenly body, which Jesus say in John 3:6
That which is born of the flesh is flesh; and that which is born of the Spirit is spirit.
Notice: He made a difference between flesh and spirit. Ask yourself that question, was you born flesh or spirit?
John 3:7
Marvel not that I said unto thee, Ye must be born again.
Back to Paul....50 Now this I say, brethren, that
flesh and blood cannot inherit the kingdom of God; neither doth corruption inherit incorruption. Notice Paul said the same thing Jesus said in John 3: 3 Jesus answered and said unto him,
Verily, verily, I say unto thee, except a man be born again, he cannot see the kingdom of God.
Notice verse 3, except a man is born again, he cannot see the kingdom of God. We have just learned something here. If you are not born again you can not see the kingdom of God. Now this is talking about the Father's Kingdom but that's another lesson for another time.
Back to Paul...51
Behold, I shew you a mystery; We shall not all sleep, but we shall all be changed, 52 in a moment, in the twinkling of an eye,
at the last trump: for the trumpet shall sound, and the
dead shall be raised incorruptible, and we shall be changed. 53 For this
corruptible must put on incorruption, and this
mortal must put on immortality. 54 So when this
corruptible shall have put on incorruption, and this
mortal shall have put on immortality, then shall be brought to pass the saying that is written, Death is swallowed up in victory.
Now this is lining up perfect with what Peter said, but we see more information add to it. We see that being born again will happen at the last trump and we will be change from
corruptible to incorruption. Also we learned a mystery and that's all will not die, but will be changed.
Paul says in
Philippians 3:21 Who shall change our vile body, that it may be fashioned like unto his glorious body, according to the working whereby he is able even to subdue all things unto himself.
And when will this take place? Again in
I Corinthians 15:52 In a moment, in the twinkling of an eye,
at the last trump: for the trumpet shall sound,
and the dead shall be raised incorruptible,
and we shall be changed. At the last trump, and not a moment before.