How long or how many up votes before a feature request is implemented?

Trying to get an idea if something is going to get worked on or not. Looking at some of the age of some of the other feature requests, I have no idea if these are even reviewed. Is there a section that lists feature requests that were implemented? Do the ones that are implemented get labeled "implemented"? Do they purge feature requests after so long? Move to a "never doing"? It be nice to know some of this.

I did a quick search and didn't see anything like this. 

Some of the ideas I saw are good but have no idea if they were implemented or not.