In modern samurai society, kannen was the official age of a person reported to the authorities such as the bakufu (Japanese feudal government headed by a shogun) or the family of lord of the domain. This custom of manipulating a person's age to report was created to bypass age restrictions set on family successions, entering government service, and gaining an audience with the shogun. The actual age of a person was called seinen.
An example of an age restriction
By Bakufu law, a samurai family with the head under the age of 17 could not adopt a child, so if the young head of the family had critical illness or died unexpectedly, the family faced the possibility of ending its line without an heir. Therefore, the age of a boy in line to inherit his family estate was reported as a few years older than his actual age.
Notice of good health
In this time period, the death rate of infants was considerably high; therefore, when a child was born, it was not required to report the birth immediately to the authorities. If a child was not registered immediately after birth, his family could report his birth after he had grown up by submitting a Jobu todoke (notice of good health) in place of the birth registration under the pretext of being hesitant to register him because of his poor health in his childhood. In this way, as there was always a gap between the time of actual birth and the time of birth registration, it was possible to manipulate the child's age by a few years.
The authorities' response
The authorities which handled the registrations were also aware of this situation, as the following examples indicate:
After an audience with a young samurai, the shogun remarked to his close aids, "What is his seinen? He seems still a child." When a roju (shogun's council of elders) was arranging a marriage for a daughter of the shogun family, he inquired the prospective bridegroom's seinen of the daimyo family from which the young man came from.