I have literally been thinking and telling others that I was 43 this year until I just had to enroll in my own healthcare and found out in the application process that I am actually 44.
I did something similar (but in a nicer way for me). The entire age of 35 I thought I was 36, and I found out on my 36th birthday that I was gonna be 36 for a second year in a row.
I decided to start counting backwards last year, forgot, and thought i was 44 instead of 45 all year :( I also lost the ability to do basic arithmetic when someone pointed out my real age.