Those who have had pets that have undergone spay and neuter in the past will likely have had this surgery performed at the age of "puberty".  This is typically between 5-7 months of age.  The selection of this timing for these procedures has been one of convenience as pets of this age can be treated as adults with respect to anesthesia.  No special anesthesia or anesthetic protocols are required.  This is also the common procedure taught routinely to veterinary medical students and thus subsequently employed in general practice.  

In the last several years there has been development of pediatric spay and neuter procedures.  These procedures are typically done on pediatric age pets (typically between 8 and 12 weeks of age).  While surgery at this age requires specialized techniques, training, anesthesia and monitoring there are several advantages to these techniques.  The main benefit is that these patients will recover remarkably rapidly.  Where most juvenile pets will be drowsy and uncomfortable for several days following the procedure, pediatric patients often go home the same day as the surgery and appear to be "quite normal" according to most owners.  The benefits of Pediatric Surgical Procedures: