Cast: timestamp to integer

Hello,

I hope it's not a question for psql-novice. ;-)

I'd like to convert timestamp and date fields to intergers.
Unfortunately cast() says it's impossible:

ERROR: Cannot cast type date to integer
ERROR: Cannot cast type timestamp without time zone to integer

I'm quite sure it should be possible somehow. After all timestamp is
(AFAIR) number of seconds counted from 1970.

I need it for example to caclulate average number of downloads of a
given file a day. For the time being I came up with an ugly solution
like this:

SELECT id, name, counter, counter/(extract(years FROM age(date_add))*365
+ extract(months FROM age(date_add))*30 + extract(days FROM
age(date_add)) + 1) AS ratio  FROM dnload_files WHERE counter>0;

I will be much obliged for any suggestions.

Thanks in advance.
-- 
 Joe