Sets and gets the age of an item

Normally, a specialized tick value of an entity is used to determine when a specific behavior of that entity should be processed. (I.E. TNT exploding after the primed entity has been first spawned.) A dropped item relies on an age variable defined in the class itself, that specifies how long it has been in the world.

This causes a problem, whereas the getTicksLived() and setTicksLived() methods inherited from the Entity class have no effect. You cannot use these methods to get/set a custom lifespan of this dropped item.

To resolve the issue, a getAge() and setAge() method has been implemented which will get/set the variable that will determine how long an item has been in the world.

Bukkit-bleeding PR: https://github.com/Bukkit/Bukkit/pull/697