However, according to "Azuma Kagami" (The Mirror of the East"), Tanetsuna was only 21 years old when he died, which means he was only 11 years old in 1218.
ところが、『吾妻鏡』によれば、胤綱の享年は21であり、建保6年当時はまだ11歳に過ぎない。