interval output format available that removes ambiguity ?

I have the need to output intervals (ages in this case).
PostgreSQL takes great care to handle months correctly (eg
take into account varying months lengths). This is only
possible if either end point or start point of an interval are
known. For post processing some of the ambiguity of what
"2 mons" means would be removed if "61 days" was returned.

Is there a way to tell PostgreSQL to return that type of
interval (eg use weeks, days, hours, minutes, seconds, ...
but not months and perhaps not even years [leap years, etc]) ?
to_char(interval, text) doesn't work as it is applied after
the fact.

Karsten
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