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?