Date arithmatic question

I have a table "t" with a timestamp column "s". I am trying to issue a query
to find all rows where s is exactly some number of days old (rounded off).

I have tried this:

select * from t where date_part('day', age('now', s)) = ?

But this only looks at the day of the month; e.g. if my parameter is "5",
then it will return all rows that are 5 days old, as well as 1 month 5 days,
as well as 2 months 5 days, etc.

I have also tried this:

select * from t where date_part('day', age('now', s)) = ? and
date_part('month', age('now', status_last_update)) = 0

But this restricts my parameter to 30 days or less; greater than 30 days and
the query doesn't return anything.

What is the correct way to express this?

Thank you,

Bryan