As you said, to good to be true, it's modern IMO. You are best off familiarizing yourself with what a 150 year old ball would look like, even under the best conditions. Here is a good source of examples:
http://www.baseballglovecollector.co...on-peel-balls/
Here is the best condition ball I think I have ever seen, and at least the leather and thread show some age.
image.jpg