Pregnancy

Hi guys, (excuse my English it’s my 3rd language grin ) so one of my daughters came to visit and after visiting she happened to have left one of her pregnancy test kits at my house and stupid me thought hmm rather than throwing it away as it was due to expire in 2 months I decided to use it and to my surprise it showed a faint line ( faint positive) shocked as I’m 66 and last time I had my period was 6 years ago. Never bled after that. Ran to the shop and bought two more test kits which showed another very very faint positive line then I decided to buy a digital one which said not pregnant. This has left me very confused. I did have sex 1 months ago without any contraception but at my age surely how can I be pregnant? If you can give me any answers as to why this is happening I’d really appreciate it