Any census information is only as reliable as the person who provided the information. Since the USA census was taken during planting season in rural areas, often children or neighbors provided the information. Many people deliberately took years off or added them on, for many reasons, like a boy wanting to go to war or a woman not wanting to be older than her husband. It is almost the norm for ages to change by more or less than 10 years between each census. This was not because the census takers got it wrong, but because they were given wrong information. It is unusual for the transcription to be different than what is written by the census taker, unless the writing is illegible. The only USA census that tends to be a bit more reliable is the 1900 because actual birth month and year were requested.