Pediatric spay/neuter is anything under 6 months of age (and as young as 6 or 7 weeks). One thing to note is that the cost of spay/neuter goes up for every extra pound the pet adds to their weight, if for no other reason than the anesthesia cost goes up...One of my dogs was spayed at 7.5 weeks, the other at 6 months.ne thing to note is that the cost of spay/neuter goes up for every extra pound the pet adds to their weight, if for no other reason than the anesthesia cost goes up... One of my dogs was spayed at 7.5 weeks, the other at 6 months.