Forms Of Address - Part Two
You can almost never go wrong addressing someone with 'Bapak/Pak' or 'Ibu/Bu,' so get in the habit of using these forms of address in all of your exchanges . . . particularly when the person you are dealing with appears to be 35 years of age or older. ("Selamat pagi, Pak Joko," Permisi Bu Rita.")
With that said, it can seem a bit "overly-formal" when a much older person addresses a younger person as "Bapak/Pak" or "Ibu/Bu."
As with "Mr" or "Sir" in English, the younger person may inform you that he/she is "not old enough to be referred to as 'Bapak/Pak' or 'Ibu/Bu,'" and request that you simply use his/her name.
This is perfectly acceptable. If you are dealing with somebody who is obviously much younger than you, feel free to simply address him/her by name. If you do not know the person's name, then do not use any form of address.
As mentioned in FORMS OF ADDRESS - PART ONE : In professional or business environments, 'Bapak/Pak' and 'Ibu/Bu' are generally used to address all colleagues (whether they be younger persons, contemporaries and older persons).