Oldest I have found in circulation was a roasted 1868 shield nickel in a coin roll a couple years back. Second oldest is the 1876 seated liberty quarter that is my profile picture back in 2016. That coin is actually what made me sign up for coin talk!
A friend of my parents got an 1841-O dime in change at a fast food place about 25 years ago. It would be a strong G, maybe VG, but unfortunately has a few pinprick looking marks on the obverse. He wasn't a collector, so he gave it to me. So now it's main value to me is sentimental.