Your wolf just has to be one of the oldest living wolves to make it on the alpha board.

Once it dies, it is taken off the list.

There's no set age, but I've never seen it below 15 years due to there being so many wolves on the entire game that are constantly born daily and die weekly(every Sunday night/Monday morning at 2:30-3:30 AM).

The prize is only a trophy that can be displayed on your den page, and you only get it if your wolf makes the top three on the alpha board.