As he was written on the right side of Munekage in "Sonpibunmyaku" (a text compiled in the fourteenth century that records the lineages of the aristocracy), it's possible that he was older than the legitimate child, Munekage, but in "Moko Shurai Ekotoba" (picture scrolls of Mongol invasion attempts against Japan) by Suenaga TAKESAKI, he was written 'Shiro jiro' (the second son).
『尊卑分脈』で宗景の右側に記されている事から、嫡子の宗景より年長だった可能性もあるが、竹崎季長の『蒙古襲来絵詞』には「城次郎」と記されている。