MaxAge is a Int64 property that represents the optional Cookie attibute that defines the lifetime of the Cookie in seconds. MaxAge contains a positive integer value or 0 (zero). 

When the number of seconds in MaxAge has elapsed, the client should discard the Cookie. A value of 0 (zero) means the cookie should be discarded immediately. 

When MaxAge contains the value GFMaxAge, a value has not been determined or assigned to the MaxAge property. 

Changing the value of the inherited Expires property will result in the MaxAge property being recalculated using the date value in Expires.

TIdNetscapeCookie.Expires