It would appear to be a common practice of women, if the difference in age of their husband was more than a couple of years younger or older. Also have seen the same practice if the woman is unmarried by her thirties, she will claim her age to be in the twenties. Their were no driver's license, health cards or requirement for birth certificates and women didn't vote in Canada until about 1919. Therefore no proof of age required.
When Canada implemented the Old Age Pension in the early 1950s my Father was the secretairy of the local school board. He received numerous request from people for proof of age 65 or greater as many people in the rural areas were born at home without the aid of a Doctor and even though since 1869 in Ontario the birth was supposed to be registered with the Township Clerk, several were not. My Father would search the old school attendance records and draft a letter certifying that the person was in grade one in year XXXX.

Jim