No, the poster said your "Messianic Gospel age" has been since Adam. Two Second Comings, one 4,000 years after Adam, one 6,000 years after Adam.
No, actually what the poster said is that the church age has been since the time of Adam. This confuses you because you don't understand the difference between what was before the advent of Christ, the Church on earth, and what the Church has become since the advent of Christ. You believe the Church came into existence when Christ came to earth a man. But as has been pointed out, the Church has always been through men/women of faith of whom the Church on earth is. Believers are the Church! Wherever or whenever we find believers, we find the Church on earth. The difference of course is that before Christ came the message about Christ, the Messiah was limited to one nation, but now since the advent of Christ the message (Gospel) about Christ is sent unto all the nations of the world.