Employment Pass Singapore

If both parties have an age difference of few months then age should not have a criteria to decide your passes. You have mentioned both have same degrees (computer science), but didn’t mention whether both of them studied from same university or not? If they are not, then one of them degree is recognised and other’s not.

Secondly, are they applying working passes now? Or is that one already working in EP at $4100 and now second person is applying then wondering why there is a difference in SAT? If one is already working under EP and the second person is comparing using SAT then it’s wrong. Each year the criteria changes (adjusted with inflation, market demand, average salary etc) even though minimum eligibility remains same.

Work pass applications are processed by MoM on a case-by-case basis. It is impossible to say for sure what the (unpublished) criteria are and where the threshold between EP and S-Pass is. Neither does one have a "right" for an EP just because somebody else with the same profile got one, too.
I suggest B should be glad that he got the chance to work in Singapore at al. After all, the differences between EP and S-Pass are small (for the employee -they are bigger for the company de to quota and levy needs).