You said that there are several examples in the Bible in which God says that something is forever, yet the thing is replaced by something else. You claim that this is because the meaning of the word often translated as “forever” in the Bible means “forever, or until the end of the age.” Can you state some of those examples?
Genesis 17:7 is one example. Here Abraham is told that the covenant of circumcision is “forever.” We, as Christians, are no longer required to be circumcised, but we do undergo a spiritual circumcision (Colossians 2:9-15, Romans 2:25-29). So the covenant of physical circumcision came to an end when Christianity began, but spiritual circumcision is still in place. Another example is the covenant with David, which, according to Psalm 89:30-37, will be established forever. There is no longer a physical descendant of David dwelling on a physical throne in Jerusalem. Of course, the promise is fulfilled by Jesus on an eternal throne in heaven. Similarly, the covenant with Moses was to be an eternal covenant. But we know that in AD 70, forty years after Jesus replaced the Mosaic covenant with a much better covenant, the temple was destroyed, and the Jews were almost completely driven from Judea. In Exodus 6:3-8 God told Moses that his people would occupy Canaan forever. In Exodus 31:12-17 it is called a covenant “forever.” Hebrews 8:6-8 also expresses the idea that the former covenant needed to be replaced by a better one, followed by a quote from Jeremiah 31 which says the same thing.
In the first and third case, the covenant was completed with the life and death of Jesus. However, there is a sense in which it continues in the spiritual antitype in the new covenant.
I hope these are sufficient.