It's a concretion with a fossilized crab of some sort in the middle, can't see too much of the crab as it's still in the concretion. I put it on a fossil site early last year and they gave me the ID.
I found it in about a foot of water in the ocean. I have looked at geological maps from the area, the rocks are from the cretaceous period. But being a concretion, who knows when it actually formed, but the actual fossil is indeed as hard as rock. So It's got to be very old. So who knows, could be 80 million years old, or could be only a thousand.. though I'm not even sure how long it takes for a fossil to.. well you know.. become a fossil. Would be awesome if it was a million years or older!!!