Those ten tell-tale signs:-
1. You don't understand what young peasants are talking about
2. You struggle to read Chaucer in weak candlelight
3. You hate rowdy taverns
4. You constantly worry that you might have the Black Death
5. You don't know or care who Blondel is sleeping with
6. You tell your wife that Crusaders seem to look younger every year
7. You struggle with new technology such as the heavy plough and the longbow
8. You find Gothic architecture too modern
9. You keep forgetting who the King is
10. You dream of buying a second hovel in France