Emperor Seimu (成務天皇) was the 13th imperial ruler of Japan. No firm date can be assigned to this emperor and he is regarded by historians as a "legendary emperor". This does not necessarily imply that no such person ever existed, just that there is insufficient material to assign him to a historical period.
... spread out with 29.0% under the age of 18, 5.0% from 18 to 24, 29.0% from 25 to 44, 24.2% from 45 to 64, and 12.7% who are 65 years of age or older. The median age is 39 ...