set_max_age
Description:
Sets this's max age to max_age.
 If max_age is -1, the cookie is a session cookie, and will expire at the end of the client's session. Otherwise, it is the number
      of seconds until the cookie expires. You can use the constants 
        COOKIE_MAX_AGE_ONE_HOUR, COOKIE_MAX_AGE_ONE_DAY, 
      COOKIE_MAX_AGE_ONE_WEEK and 
      COOKIE_MAX_AGE_ONE_YEAR (or multiples thereof) to calculate this
      value. (A value of 0 indicates that the cookie should be considered already-expired.)
(This sets the same property as set_expires.)
Parameters:
| this | a Cookie | 
| max_age | the new max age |