How to return a set of rows from this function?

I am new to Postgres functions and have a table with the following structure:

CREATE TABLE options.options (
  delta double precision,
  gamma double precision,
  rho double precision,
  theta double precision,
  impvol double precision,
  value double precision,
  vega double precision,
  id bigserial NOT NULL,
  date bigint,
  ticker text,
  callput text,
  chg double precision,
  maturity integer,
  symbol text,
  strike double precision,
  implied double precision,
  last double precision,
  vol double precision,
  ask double precision,
  bid double precision,
  CONSTRAINT options_pkey PRIMARY KEY (id)
);

And I am trying to build the following function:

CREATE OR REPLACE FUNCTION generate_term_structure_by_moneyness(arg_ticker text
                                  ,arg_date integer
                                  ,arg_underlying float
                                  ,arg_lower float
                                  ,arg_higher  float)
  RETURNS SETOF varchar(250) AS -- declare return type!
$BODY$
BEGIN -- required for plpgsql

   RETURN QUERY
    select maturity,avg(Implied) from options.options 
    where ticker=arg_ticker and date=arg_date and strike/arg_underlying>arg_lower 
    and strike/arg_underlying<arg_higher group by maturity order by maturity asc;

END; -- required for plpgsql
$BODY$ LANGUAGE plpgsql;

The issue I am having is the following error when trying to run the following query:

Query

select * from generate_term_structure_by_moneyness('TQQQ',20151221,120.2699,.98,1.02)

Error

ERROR:  structure of query does not match function result type
DETAIL:  Returned type integer does not match expected type character varying in column 1.
CONTEXT:  PL/pgSQL function generate_term_structure_by_moneyness(text,integer,double precision,double precision,double precision) line 5 at RETURN QUERY
********** Error **********

ERROR: structure of query does not match function result type
SQL state: 42804
Detail: Returned type integer does not match expected type character varying in column 1.
Context: PL/pgSQL function generate_term_structure_by_moneyness(text,integer,double precision,double precision,double precision) line 5 at RETURN QUERY

I believe the error is coming from returns setof but I am unsure how to cater to this result type.

In pseudo code the returned data is expected in the form of:

[int,float; int, float; ...]