This verse is not a millennial reign verse:
And in the last days it shall be, God declares, that I will pour out my Spirit upon all flesh, and your sons and your daughters shall prophesy, and your young men shall see visions, and your old men shall dream dreams.
The "last days" refers to the time from the day of Pentecost to the end of the age of Grace. This time. A time when apostasy is growing, persecution is enlarging, and believers will be without the Scriptures in their hand but must rely upon that implanted in the heart, by the memorization and work of the Holy Spirit.
I was active during the years when the communist block regularly imprisoned pastors and preacher who would not submit to state control.
More often these would share how God would visit them in the midst of the most stress filled times, and remind them of the Scriptures, at times these didn't know if they dreamed or were awake.
The Holy Spirit is poured out on all flesh as Christ said, "And when he (Holy Spirit) comes, he will convict
the world concerning sin and righteousness and judgment:..."
This coming of the Holy Spirit was recorded in the book of Acts.