If I list all the faithful patriarchs from Adam through Abraham (found in Genesis 5:3-32 and Genesis 11:10-22) and add Isaac and Jacob, the total comes to 24. Since we are never told how long the 24 Elders have been in Heaven or when they got there, wouldn’t their number more likely be composed of these patriarchs rather than being representative of the Church?
The 24 Elders were not mentioned by Isaiah, Ezekiel, or Daniel, all of whom saw visions of the throne of God. Only John saw them, and he was taken forward in time to the day of the Lord to do so (Rev. 4:1-2).
From this we can reasonably conclude they weren’t there in Old Testament times, and perhaps are not even there yet.
But the patriarchs were never promised what the Church has been promised.
They won’t be Kings or Priests (Rev. 5:9-10), they won’t be seated with the Lord in Heaven (Ephes. 2:6-7), and they won’t reign with Him as as co-heirs of His inheritance (Gal. 4:4-7).
In Hebrews 11 the writer was recalling the great men of the Old Testament. Some of the patriarchs were included in his “Hall of Faith”. He said,
“These were all commended for their faith, yet none of them received what had been promised. God had planned something better for us so that only together with us would they be made perfect” (Hebr. 11:39-40).