Apartment is literally divided in half with gates

Hello, I am new to the site and have a similar issue with my two kids. I have a resident 13 yr old spayed female calico Trinity (T1) and a new former stray Tristan (T2) who is neutered, almost 2, and an alpha male. I have had Trin for about 8 years and had them as a pair for 7 months. my apartment is literally divided in half with gates. Tristan will run at Trin, she will hiss and run away. He will chase her and park himself right in her path of escape from wherever she has hidden. Paws start to fly, hissing on her part only. She will remain in hiding even after he has been removed. BTW, removing him from her location is met with redirected agression, all teeth and claws. They have progressed to being able to eat in front of each other with a gate between, but as soon as the gate is removed, he runs after her. If she walks by his gate he will reach out at her or stare at her, no hissing ever on his part. I switch them between gated areas to avoid territoriality and mingle scents. I spend equal amounts of time with each kitty. On a 1 to1 basis, Tristan and I have bonded nicely. Initially he could not tolerate petting and bit me almost daily. Now he allows full body brushing, knows his name, comes when called, and will come up in my lap on his own (all done by clicker training). He bites only when I have inadvertantly pushed one of his "buttons". He is a sweet boy with feline PTSD.

I am aware that the age mix is not ideal. I was not aware that Trinity would dig in her heels so much until I got Tristan since Trin had lived with her sister for several years until her death. I have been to a behaviourist and tristan is on the standard feline dose of Prozac which has really helped him and he is tolerating it well. He is healthy and incredibly smart (Maine Coon). Yes, the size mismatch is a concern. All in all not an ideal situation, but I am not willing to consider giving up either one. I have no children and have all the time in the world for these two. Any comments? Suggestions?

Tristan will run at Trin, she will hiss and run away. He will chase her and park himself right in her path of escape from wherever she has hidden. Paws start to fly, hissing on her part only.

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Now, my situation could be totally different, but my cats Eko and Emily (the gray and black cats in the avatar photo) play this game all the time.  Granted, Emily is always the one under the furniture hissing.  But I watch all of their interactions carefully to make sure she isn't feeling bullied.  She initiates chases with Eko at times and doesn't show signs of fearing him or stress. 

She will remain in hiding even after he has been removed.

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This might be the key to whether she is really traumatized by it.  Emily will hide for just a minute or so after Eko walks away.  Then she comes out.  Now, both of them are young, 2 yrs old, and they have enjoyed playing together since they were teenage kittens.  Emily just really likes to raise a ruckus (with the hissing) when Eko gets the better of her in a game.

I guess I bring up my own experience just to suggest that maybe it is an attempt at play on Tristan's part.  What would happen if you didn't intervene?   It might be worth exploring. (Or instead of removing him could you distract him with a wand toy?)   Of course, a 13 yr old cat might be truly stressed by his attempts at play.  I'm not suggesting you let her be bullied, just suggesting another way of looking at it.  Good luck with them.

Edited to add this thought....With a young cat and older cat, I'd make sure the younger cat gets plenty of interactive play with you to get out some of his hunting, chasing urges.  Some interactive games my cats have liked include, dangling feather on a string toys for them to kill, laser pointer, throwing their favorite ball for them to chase, etc....  None of them can resist wand type toys if I make it a game of hunt....having the toy on the end go around corners, dart across their field of vision and stuggle to get away when they capture it.  Also, if the older cat enjoys such games it could help build her confidence.  She might be more confident in her relationship with Tristan as a result. 

Hi txcatmom,

Thank you for the suggestions. I have tried letting Tristan out while Trin is in a carrier and I am within reach. He sniffs the carrier screens with his face right up against. She takes a swipe and hisses. Perhaps if I continue to do this she will get used to him being so close and he will get used to her hissing. If only he would just walk away when she hid. I am fighting his instincts and natural urge to play. I agree that helping him burn off steam is very important. He has every toy in creation and gets very easily bored. It is a challenge to find new ways to entertain him. Trin is very easily entertained and also likes to play. I have not tried them out together in some time, perhaps I'll give it another shot.

It does get frustrating though, having to spend time with each kitty separately, and constantly meeting resistance while trying to integrate them. I need to get the idea of some time limit out of my head and just take it one day at a time. I joined this site in the hopes of not only getting advice, but moral support for the long haul. I appreciate the support and will post updates.