His older brother is much older than he哪里错了

应该是

His elder brother is much older than him. 吧。。。

elder 和 older用法稍有差别。。。

呵呵。。。我来告诉你。
语法应该没有错，只是句意 好像很废话。。。
他的哥哥比他大许多。

他哥哥的年纪比他大
than + 第三人称 him
所以应该是
His older brother is much older than him

应为
His older brother is much older than him.