Box says 8 weeks old and up, no mention of weight other than under 5lbs. Ratchet is 2.1lbs and 7 weeks old, do you think he's big enough to use it? He's bigger than most of my fosters at 10 weeks. I'm not normally one for flea meds since my kitties are indoor only, but I have a flea infestation right now. Every time I treat the apartment and Bootsie all the fleas jump on him. Dawn bath and flea comb later, there still ends up being a few on him. And since I'm on the subject of weight, my vet said to bring him in to neuter at 2lbs. Now that he's over 2lbs, is that too small for a neuter at 7/8 weeks?