Oh ok.
So, for elephants, the earliest use for them was in 4500 BC, according to Wikipedia. So, let's say they're unlocked in the ancient era with the Bronze working technology.
I think converting the ivory resource to a strategic resource would be fine. Since strategic resources need a tech to unlock, let's say the "elephants" are revealed with trapping.
In the Ancient/Classical eras, they're just stronger horsemen that are slightly slower. Obviously have the feared elephant promotion. However, they are much more expensive to build.
I think that would be a good starting point.