This is a continuation for my answer to Diego (that cute little boy!). I would say that this is something that you don't have to worry about at all, but while some reddening of the gums is normal at teething time, if it continues after the teeth have grown in, if the breath becomes foul, and if the teeth seem to be rotting even though the cat is still not yet an adult, you might consider asking your vet about gingivitis/stomatitis, a rare but very painful disease. I know I sound like Typhoid Mary going on about this, but when I got my Harvey, there was some doubt that he had this disease; he had his gums scaled, and now has a faint pink line at the gumline, but (so far!) perfectly healthy teeth. This is a rare but not unheard of condition; just be aware that it exists, and watch the condition of your cat's gums. Irritated gums at teething time, however, are normal, and "juvenile gingivitis" will resolve itself in time. Don't worry, just be aware that this condition exists.