This comment:
// Set to the index in the cooldown array (see below) that represents
// the current cooldown duration for this Kitty. This starts at zero
// for gen0 cats, and is initialized to floor(generation/2) for others.
// Incremented by one for each successful breeding action, regardless
// of whether this cat is acting as matron or sire.
uint16 cooldownIndex;
says that cooldownIndex should be initialized to floor(generation/2) for all kitties with generation > 0. However I haven't found any code that implements this functionality, all kitties regardless of generation seem to start at 0.