How much time has passed since the fall of the Roman Empire?

We claim it was many centuries ago, but what if the Roman Empire fell in the mid 19th century and everything is a lie? Think about it. The oldest known living person is Misao Okawa, born March 5, 1898. Nobody's left to even know it was a lie. HOW CAN YOU PROVE IT!?! Maybe we're in a computer simulation made BY THE ROMANS!