Wookeepedia says sometime before 32 BBY. Does anyone know where that number came from? That would make him 26-28 when he met Thrawn and 42 + when he went to the Chiss Ascendency. Doesn't that seem a little old for Elie's persona? In the academy at 26? Vah'nya (22) flirting with Eli (42). BUT I suppose if Chiss mature faster, they might be developmentally the same age.
This is basically the same question as your other thread asking about when Thrawn's exile was - the year is never explicitly stated in Thrawn. However, I'm not sure where your math is coming from. Assuming Eli was born in 32 BBY, he would be 32, not 42, during Thrawn: Treason, which we know to be around 0 BBY.