Her elder brother is five years her senior.

她的哥哥比她大五岁。

senior有年长的意思，也指年纪叫大的人。钢材那句话相当于 Her elder brother is five years older than she.

上面的那句话也可说成：

Her elder brother is five years senior to her.(注：这句的senior是形容词，表示年纪较大的)