Performing INSERT from a Trigger fired function

I want to be able to capture changes to a db with the use of triggers. I have created a simple db to test the methods to do this. When I change the age in this example, I get the error - "cashe lookup failed". I drop the trigger and the function before I make a change to the function and create the function and then the trigger to test changes. I always get this error. The scripts I use are attached. Thanks in advance the any ad all input... I love this stuff!

CREATE TABLE "consumer" (
"name" varchar(35),
"age" int4
);
----------
CREATE TABLE "changes" (
"name" varchar(50),
"oldage" int4
);
----------------------------
CREATE FUNCTION "save_change"() RETURNS "opaque" AS
'BEGIN
INSERT INTO changes( name, oldage )
VALUES( new.name, old.age );
RETURN new;
END;
' LANGUAGE 'plpgsql';
-------------------------------------------------
CREATE TRIGGER "xs" AFTER UPDATE ON "consumer" FOR EACH ROW EXECUTE PROCEDURE save_change()
--------------------------------------------------
DROP Trigger "xs" on "consumer" ;
------------------------------------------------
DROP FUNCTION "save_change"();

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