I've never heard of a vet suggesting to wait till a female has gone into heat. Heat cycles aren't good for a cat in the long run unless they are to breed. Most vets fear the early spay/neuter because they are scared the cat will not grow properly due to lack of hormones plus the risk of the anesthsia. Males and females should be spayed and neutered around 4- 6 months. Thats when most vets feel comfortable. Some may do it as early as 12 weeks. Some say it calms them some say it dosen't. Kittens will be kittens I guess.