Mas itu ramah; dia menyuruh kami menepi dulu karena jalanan depan stasiun sempit.

Mas is a common Indonesian form of address for a young adult man, especially in Java. A native English speaker might think it is part of the man’s name, but here it is more like brother / sir / young man / mister, depending on context.

In this sentence, Mas itu means something like that guy / that man / that driver in a polite, natural Indonesian way.

A few useful comparisons:

• Mas → for a younger man
• Mbak → for a younger woman
• Pak → for an older man / Mr.
• Bu → for an older woman / Mrs./Ms.

So Mas is not being translated literally as older brother here, even though historically it comes from that kind of kinship term.

Itu here means that. So Mas itu is literally that mas / that man.

In Indonesian, itu often comes after the noun:

• orang itu = that person
• rumah itu = that house
• Mas itu = that man / that guy

This is different from English, where that usually comes before the noun.

In this sentence, Mas itu identifies a specific person already visible or already known in the conversation.