Although you may have been born in the United States as were your parents and your grandparents, you might find that you have relatives or ancestors that lived in Canada. The Canadian census images that are currently available for viewing will then be of interest to you.
I have looked at hundreds of US census images. This data is not always reliable as I found on more than one occasion that the age of the same person from one census to another are not always 10 years apart. One of my relatives was less than ten years older in the next census to the point that she was almost the same age in one census as she was 30 years before.
However, as you come across records and find that you have a year's difference in the birth year of a relative who lived in Canada and in the United States, it may be due to the difference between the meaning of the age recorded in a census between the US Census and the Canadian Census.
The instructions to the enumerator of the US census has been since the 1850 census to record the age of the individual at his/her last birthday. I looked at so many US census images that I assumed that the age in the Canadian census was the age at the last birthday. I was wrong!!!
When you find a relative in a Canadian census, do not assume that the age is the age at the last birthday. You will be wrong as was I. After enough times that I found a relative in a Canadian census whose age was a year older than I expected, I decided to look at what that data meant. A little research revealed that the age in the Canadian census is the age at the next birthday.
If you are looking at census images for countries other than the United States, be sure to understand what each data point means. Do not assume that you know.