Help-found new kitten!

Hi everyone! This is my first post and I'm really worried! Here's what's going on:

In July of 2008 my daughter's boyfriend was working in a vet clinic when an abandoned newborn kitten was dropped off. We agreed to foster it until it was old enough to be adopted. He was only days old so we bottle fed him and tried to fill in for his real mother as best we could. Needless to say that kitten (Iggy) is still with us Today Iggy is a healthy adult male cat. He has been neutered. Til now our only problems with him have been a few play-aggression issues which, from what I've read, seem to be fairly common with kittens abandoned/orphaned at such a young age. In general he is friendly and playful but not super affectionate. He gets along very well with our two dogs.

Iggy is now around 17 months old and yesterday my husband found a very young kitten that appears to be either feral or abandoned. The kitten doesn't seem wild-very friendly and comfortable with people and both of our dogs (Annie/border collie/12 yrs and Jack/Shih Tzu/6 yrs). He hasn't been to the vet yet-we've got a Wednesday appointment-so I'm not letting anyone get too close. The dogs, so far, are fine with him.

So, question #1

How old do you think our new lttle guy is?
It's eyes have almost completely changed from blue to green. It's walking well (if a bit clumsily) and can climb out of the litter box and up the back of our sofa. He/she is eating canned cat food mixed with a little milk replacement mixed in. The tail still seems a bit on the short side though.

Question #2 (and the REAL problem)

At first Iggy (the older cat) seemed more curious than anything. This morning, however, he began hissing and growling at both the kitten and me. Iggy has always tended to play a bit rough but today he seems different, very upset and NOT playing around. I tried to pick him up like I do all the time and he attacked me. This wasn't a play type attack-Igs was deady serious! I'm trying to follow the information I've gotten on various web sites about introducing a new cat-different feeding and sleeping areas, different litter boxes, etc. When I can't carefully watch the kitten he is in a cat carrier.

Iggy will still come into the room where the new cat and I are but he gets very aggressive if I try to approach him.

What do I do? We like this new kitten but I don't want to lose my Iggy in the process!

Thanks and sorry so long!

Jennifer

Thanks for the replies!

We have been keeping new kitty and Iggy separate. They've never actually come face to face-it's me that he's attacking! The only room that works for the kitten is, unfortunately, Igs' litter box room. I moved his box and he's using it so that's okay. Iggy does seem a bit calmer today and he slept in my bed last night so I guess he just needs to get used to things.

I do have another question. Iggy has never been around another cat. He was found when he was only a few days old. Someone had put the whole litter in a garbage bag and thrown it in a ditch and Igs was the only survivor. He has some very quirky and un-catlike behaviors. Sometimes he seems more like a dog! Do you think that will effect how he reacts to a new kitty?

Baby kitty is seeing the vet in a couple of hours. We had to put it off due to an out-of-town commitment.

Jennifer

Iggy is doing much better today. I can pick him up and he's condescending to sit in my lap at the moment-very much his old self-he's always been more of the kind of cat that you play with rather than snuggle. The kitten came home from the vet with a clean bill of health. I still haven't let them meet yet. I just hate to freak Igs out again.

Jennifer