Adding dates in plpgsql

I have a trigger that needs to do some addition to dates,

CREATE FUNCTION update_dis_record () RETURNS OPAQUE AS '
DECLARE
tmpYellow INTEGER;
tmpBan_Starts timestamp;
BEGIN
tmpYellow := NEW.yellow % 5;
tmpBan_Starts := now + "14 Days";
IF tmpYellow = 0 AND NEW.yellow <> 0 THEN
NEW.length := NEW.length + 1;
NEW.ban_starts := tmpBan_Starts;
END IF;

IF NEW.ban_starts <> null THEN
NEW.ban_starts := OLD.ban_starts;
END IF;

RETURN NEW;
END;
' LANGUAGE 'plpgsql';

The line "tmpBan_Starts := now + "14 Days"; " doesn't work obviously, but
what is the correct way to ad 14 (or any number of ) days to a date with
plpgsql?

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