Some folks have asked over the years "Where did this idea of a previous age come from?" Some folks point to Peter as he is the only one in scripture that really talks directly about it....as you have pointed out. But....Moses, Isaiah, Jeremiah, Ezekiel, Jesus, Matthew, Luke, John and Paul all allude to a previous social order prior to Adam.
In [2 Peter 3:6-7] we have a definite statement that there was a social world before Adam, which is called, "the world that then was." The Greek word for world is "Cosmos", meaning social system. This social order had to be before this one we now know, or it could not be called "the social order that then was." That it was one which existed before our social order since Adam, is clear from the next statement about "the heavens and the earth, WHICH ARE NOW." The two statements, "the world THAT THEN WAS" and "the heavens and the earth, WHICH ARE NOW" prove there were two separate social systems on Earth. One was BEFORE the one WHICH IS NOW, and the other, AFTER the one THAT THEN WAS. If it can be definitely proved that "THE WORLD THAT THEN WAS" refers to a social order on Earth before the present heavens and the Earth WHICH ARE NOW, then it would be forever settled that there were inhabitants before Adam.
1.Men are never spoken of in Scripture as "spirits". Man has spirit, but he is not "a spirit", for a spirit hath not "flesh and bones". In this life man has "flesh and blood", a "natural" (or physical) body. At death this spirit "returns to God who gave it" (Ps.31:5, Eccl 12:7, Lk.23:46, Acts 7:59). In resurrection "God giveth it a body as it hath pleased Him" (1 Cor.15:38). This is no longer a "natural (or physical) body," but a "spiritual body" (1 Cor. 15:44).
He goes on about the angels that left their habitation....
6.Returning to 1Pet.3:19, the expression "the spirits in prison" cannot be understood apart from the whole context. The passage commences with the word "For" (v.17), and is introduced as the reason why "it is better, if the will of God should (so) will, to suffer for well-doing than for evil-doing. FOR (v.18) Christ also suffered for sins once (Gr.hapax)-a Just One for unjust ones-in order that He might bring us to God, having been put to death indeed as to {His} spirit." This can refer only to His spiritual resurrection body (1Cori 15:45). In death His body was put in the grave (or sepulchre,i.e. Hades), Acts 2:31; but not until His spirit was reunited to the body in resurrection could He go elsewhere. And then He went not to "Gehenna", or back to Hades, but to Tartarus (2 Pet.2:4) where "the angels who sinned" had been "delivered into chains". To these He proclaimed His victory.
This writer, E.W. Bullinger, believes the "prison" Christ went to was to that of the fallen angels. Apparently not to offer salvation (as I thought to those of Noah's time) but to proclaim victory.
Your friend......Ping