I didn't find this coin, but my partner did. It was a 1788 Mexican Reale. He found it in a dry Creek bed
here in Ohio this past summer. I was hunting the same creek bed when he found it. Boy what a surprise that was.
I don't know what my oldest coin is that I found with the ACE 250, I have found many 1800 coins with it. I guess the 1853 half dime would come in close. I and my partner both found 2 flying eagle pennies last year. Boy what a fun detector this is to use. For the nay sayers, I hope they keep using those top of the line, top dollar detectors. LOL
I can't find the picture of the 1788 coin, but if I do, i'll send it.
HH, Ringfinder
P.S. I just found a 1836 Large Cent that I found this year also.