Rebecca, thanks for using our service.
The good news is whether you are certain on the sex of your cat or not, the veterinarian will be able to do the surgery to sterilize your pet either way. And they've seen enough genitals to be certain upon exam.
At 9 months of age, you should be able to determine if there are testicles or not. Cats very seldomly have retained (undecended) testicles.
I'm using pictures of sphynx (hairless) cats so that you cat EASILY see what you're looking for.
This is a male cat. The testicles are going to be obvious no matter how you look at him:
This is a female (there's obviously something missing):
Here's a more furry version of the same thing. A male (green arrow denotes testicles):
And a female:
One surefire way to know if your cat is a female without having to look is whether or not she's ever gone in to heat. It's very likely that at 9 months of age, you'd have noticed your cat crying and rolling around, being overly affectionate, cleaning her genitals repeatedly and trying desperately to draw attention to herself. She may also paddle her back feet, as noted in this video:
(http://www.youtube.com/watch?v=GO7_iSQLscc)
Or the behaviors denoted above:
(http://www.youtube.com/watch?v=-ZIm07_cj9E)
If you honestly believe that there is a "pouch" area, feeling two marble sized testicles would indicate your cat to be a male. However, most owners prefer to leave the "hands on" approach to the veterinarian.
If my answer has helped you, please click accept. If not, reply. I personally don't get paid for my work unless you click accept. Thanks so much and good luck!
Veterinary Nurse
8 yrs experience with animals, 3 in emergency med. Owner of 3 APBT and 3 sphynx