Because aionios (“eternal”) modifies both punishment and life in Matthew 25:46, it stands to reason that the same quality and temporal connotations are in view. That is to say, however long the life extends is how long the punishment lasts; the durations are identical. It is grammatically unsuitable to drive a wedge between the two uses of the term eternal in Matthew 25:46, suggesting that one refers to endlessness (eternal) and the other to temporal limitation (aeonial)… Since it is clear to say that the eternal life is temporarily unlimited it follows that eternal punishment is also temporarily unlimited.
Scot McKnight