Cain is the first human to be born physically,for Adam and Eve were created without parents,although born by God in that they were created.
The man Christ Jesus is the first born of the dead.
The man Christ Jesus could of not been born again,for He was sinless,and did not need to be born again.
John the baptist could not have been the first to be born again,although he received the Spirit from birth,which was not to save him,but give him power to grow up rightly,and prepare himself,to pave the way for Jesus.
John the Baptist was not saved the whole time he was on earth,for Jesus did not shed His blood yet,which is why Jesus said that born of women there has not been a greater than John the Baptist,but he that is least in the kingdom of heaven is greater than him.
Peter was the first to be born again,for he was given the keys to the kingdom of God,and Jesus said when you are converted strengthen your brothers,and Peter was the first human to be built upon Christ,the chief cornerstone.
1Co 3:9 For we are labourers together with God: ye are God's husbandry, ye are God's building.
1Co 3:10 According to the grace of God which is given unto me, as a wise masterbuilder, I have laid the foundation, and another buildeth thereon. But let every man take heed how he buildeth thereupon.
1Co 3:11 For other foundation can no man lay than that is laid, which is Jesus Christ.
Mat 16:15 He saith unto them, But whom say ye that I am?
Mat 16:16 And Simon Peter answered and said, Thou art the Christ, the Son of the living God.
Mat 16:17 And Jesus answered and said unto him, Blessed art thou, Simon Barjona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven.
Mat 16:18 And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it.
Mat 16:19 And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven.
No other foundation can be laid but Jesus Christ,and Peter is the first person added to the kingdom,and built upon Christ,and then it goes from there is order of who is born again,building upon each other like a building.
Peter is the first to be born again,for he was the first person to be added to the Church,being built upon Jesus the chief cornerstone.