Resting in the fridge is a good idea for all chickens...but if the ones you are cooking are 2 years old they will still be tough if you roast or fry them. Might want to consider some slow cooking instead and the best chicken and dumplings ever!!
And in addition to age, chicken goes into rigor mortis after it dies. It is recommended by a lot of folks to let them sit in the fridge for two or three days. They go out of rigor in that time resulting in a more tender bird.