因该是 his .因为是 your age 和 his age 作比较
这句话相当于 My age is the same as his age.为什么老师说是him？可我觉得是his，但好像我错了，不知道为什么我还是坚持是his.这句话还可以翻译成: We are the same age. 你可以再和老师探讨。