I had Gulliver done when he was 4 1/2 months. he was already nearly 5 pounds and did just fine. Only had to wear the cone for about four days and never needed the pain meds they sent us home with. now at almost 8 months he's still a squatter and hopefully (please please please) always will be. When we did the neuter our vet did a complete blood workup just like they do for dentals and their semiannual check ups.
by the way, if you don't already have one, get one of Mom to Hot rod's kiss-e cones. they're awesome and sooooo much more comfortable for the babies than those plastic cones you get at the vets. Lots more stylish too
.