In the NT when it refers to Jesus as the firstborn (Rom 8:29, Heb 1:6 &
12:23, Rev 1:5, Col 1:15,16,18) does that mean that he is first to be
“born again” by his baptism?

A great question! To answer this question, one must
understand what “firstborn” meant to the Jews. For the Jews, the first
born son was the one who automatically became the head of the family and
received a double portion of the inheritance. The position of the
firstborn is one of the issues of dispute between Jacob and Esau. In
Genesis 25, Esau sold his birthright for a bowl of stew. In Genesis 27:
Jacob tricked Isaac into giving his the blessing of the firstborn son,
making him ruler over his older brother.

This is the idea behind the phrase “firstborn” when it is used
in the New Testament. In the New Testament, firstborn means preeminent,
first, head, greatest amongst the group to which it refers. So, in Romans
8:29, Jesus is the firstborn of the believers in many ways. He is the
greatest, the preeminent, the leader of the brothers. Hebrews 1:6 calls
Jesus the first born in the broadest possible sense. He is the head over
all, including the angels (in the context of Hebrews). In Hebrews 12:23,
“the firstborn” is used as a title for Jesus.

Most interesting (at least in my opinion) is the references to
Jesus as the firstborn from the dead, in Revelation 1:5 and Colossians
1:15. Jesus is the firstborn from the dead because of his resurrection
from the dead. Jesus was not the first to be resurrected (the Shunnamite
woman’s son, Jairus’ daughter and Lazarus for example), but he is the
first to be resurrected to a spiritual body which will never decay. Note
that all those mentioned above were resurrected in their original,
physical bodies. All of them died a physical death later. In that sense,
Jesus is literally the firstborn from the dead. He is also the firstborn
from the dead in the greater sense. He is the greatest, the preeminent,
the presiding one over all those who ever have been or ever will be raised
from the dead to eternal life.

By the way, Jesus was baptized by John, of course, but it
would be a mistake to think of him as being born again when he was
baptized. Jesus did not need to be born again. He had never died. Being
born again implies participating in the death and resurrection of Jesus
(Romans 6:2-7), and Jesus certainly did not need to do that. He was
baptized, “to fulfill all righteousness,” but not to be born again.

For more on this topic, there is a section on Jesus as the
firstborn by virtue of being resurrected on the Feast of Firstfruits in my
new book. Click on From Shadow to Reality The relevant section is in
chapter seven. Go down to the section on the Feast of Firstfruits.

John Oakes