http://www.ageofconsent.com/japan.htm
Age of majority
The Article 3 of the Japanese Civil Code states that the age of majority
is twenty (20) years old.

Age of consent for sexual activity
The Article 177 of the Penal Code puts the age of consent for sexual
actitvity at thirteen (13) years.

Age of consent for marriage
Articles 731 and 737 of the Civil Code provides that the age of consent
for marriage is eighteen (18)
years for men, and sixteen (16) for women.

But when a minor wants to get married, he or she needs the consent of his
or her parents.

-HJC