I'm setting up a an old bearcat bow for a Christmas present to someone who draws about 24" . Should I set the brace height a bit lower than what it seems to like at my 28" draw?

No, it should be set the same. Someone will be very happy with your gift!

Like Bjorn said, No.  The brace height is wherever the bow shoots best and draw length should make no difference.

Thanks, the bow's a big hit, the kid shoots better than me LOL.