Elapsed time between timestamp variables in Function

Hi !

I saw previous postings about elapsed time between 2 timestamps, using SELECT EXTRACT...
I have similar question, but it's not in a select statement, but between 2 variables in a function.

To keep it simple, I have 2 variables, let's say A and B, both TimeStamp. Now I would like to know the absolute value of elapsed seconds between the 2 timestamps. Has to be absolute value, because can be positive or negative, depends if A > B or A < B.
I tried with age(A, B), but that gives me something like 00:00:01, not really numeric value for number of seconds.

Many thanks in advance !
Nico