Idioms are notoriously difficult to translate. When they occur in isolation, they are a little easier since you can just find an English expression that carries the same meaning. But when they fit into the context of the passage, they are more difficult.
Paul tells the Corinthians, “we speak the wisdom of God; a wisdom that was hidden in mystery and that God had determined before the ages (πρὸ τῶν αἰώνων) for our glory” (1 Cor 2:7; see NRSV; NLT).
To most English readers, “before the ages” is meaningless. What ages? The Ice age? Which one?
To someone who understands the linear nature of the Jewish concept of time, it is understandable. We live in the first age, heaven is the next age, and so “before the ages,” more properly, “before this age,” makes good sense. God’s determination was made before this age began. But it makes no sense to someone less trained.
So the NIV tries to help us with “before time began.” Of course, this introduces a concept totally foreign to the passage, as if it were teaching something about time before creation. I know we are often taught that there is no time before creation, but I find it impossible to understand the idea that at some point “in time” there was no time, no sequencing of events.
The KJV is actually better. “Before the world,” which clearly means “before the world was created” (also TEV).
The real problem comes in the next verse. “None of the rulers of this age (τοῦ αἰῶνος τούτου) understood it, for if they had, they would not have crucified the Lord of glory.”
Certainly the word connection is significant. God made this determination before the world was created, and the rulers of this world failed to understand it.
These types of connections are often loss in a more functional equivalent translation, and especially then there is an idiom involved. So I actually like the KJV here. “But we speak the wisdom of God in a mystery, even the hidden wisdom, which God ordained before the world unto our glory: Which none of the princes of this world knew.”
The NASB keeps the concordance was well. “[B]ut we speak God’s wisdom in a mystery, the hidden wisdom which God predestined before the ages to our glory; the wisdom which none of the rulers of this age has understood” (see also the ESV).