Get another function to return timestamp in PostgreSQL
Your function is insecure and vulnerable to SQL injection:
SELECT f_last_update1('sometable; DROP TABLE sometable; SELECT current_timestamp');

Use
CREATE OR REPLACE FUNCTION f_last_update1(
   IN  nomSchema text,
   IN  nomTable text,
   OUT updated timestamp)
  LANGUAGE plpgsql AS
$func$
BEGIN
   EXECUTE format(
              'SELECT max(updated) FROM %I.%I',
              nomSchema,
              nomTable
           )
      INTO updated;
END
$func$;