When purchasing game birds age is an important consideration as it will often determine the method of preparation and cooking. 

Mature birds game birds have jaws that are set.  If you can lift the  bird by its lower jaw without it breaking , it is an older bird.

Young birds have clean soft textured feet, pliable breast bones and rounded spurs on the legs. 

As birds age their breast bone becomes hard and brittle and their meat tougher.