Cat won't stop trying to mate

We did the proper separation/introduction when we brought home a young female kitten to befriend our boy. They got along fine at first, then a few days later his behavior changed and I caught him trying to figure out how to mate with her. We separated them again and got him neutered. Its been a few weeks and when we let them near each other he still just wants to mate. She's a lot smaller than him but she tries to fight back and I'm quite afraid it will turn ugly or she will get hurt. Will he ever stop trying to mate with this little kitten? Will I have to re-introduce them?

Hi clmgordon,

First things first, has the female kitten been spayed? Female cats can have their first heat cycle as young as 5 months. The first heat is often a silent heat, which means you won't realise she is ready to mate.

Male cats still produce sperm and are able to father kittens up to one month after being neutered, so it would be a good idea to get the kitten spayed as soon as you can.

Mounting and scruffing can be signs that your cat is trying to assert dominance over the female kitten. Male cats do this to each other too. Once the kitten is full grown and able to put him in his place this should stop. For now it would be a good idea to keep them apart unless you are able to supervise. Getting the cats to play together with a wand toy, so they are focused on the game rather than each other, could help.

Have you tried using a Feliway diffuser? 

No, she is not spayed yet and she is only about 3 months old. We do have an appointment made to get her spayed but it will be a few weeks. I had hoped that as long as I got her spayed before 4 months this wouldn't be a big problem.
Also, I've not tried the diffuser but I have tried calming collars and sprays, which didn't work.
He yowls at her door all day and night and tries to break into her room, he wants to mate with her sooo bad. I guess we'll continue to keep them separated, but when can I expect this to end or what can I do to help it along in the meantime?

Thanks for your help, keeping them separated has made things pretty difficult lately!

It can take upto 3 months for his hormones to settle down unfortunately.
See, although he's been neutered those male hormones are still raging in him. As his hormone levels start dropping he will get calmer over the weeks.
- not brilliant when you've got keep them separated & a yowling cat too !
But at least you know it will get better

How old is he?  Had he ever mounted stuffed animals or pillows before this?  Usually a month is pretty much all is needed to get rid of residual hormones, unless they are older and had "experience."  And sperm can only live so long.  So, that should be out of his system, too... If it's been a month.  My thinking is that contrary to belief, neutering only makes it so they can't produce babies but it doesn't always mean they lose interest entirely.  I have a male that was neutered 3 years ago but still tries to do the deed with my spayed female. 

Also, another thought... Where did you get the female kitten?  Often people or rescues will say they are younger to make them more appealling in the adoptiong process.  (Everyone wants a kitten, the younger the better.)  So she MAY be older.  And it is unusual but not unheard of for them to come into heat at 3 months.  I would ask my vet to weigh her as weight counts more than age and see if you can push up her spay surgery date.

He's about 7 - 8 months, he has no experience though. She could be older than 3 months, it just seems unlikely as she is very small.
Yeah, I kinda figured he would continue to have that urge and we would have to let them work it out when she gets older. Guess I just have to be patient!

Regardless of age female cats can go into heat early. If they didn't go into heat so early there probably wouldn't be as much of a need for early spaying (in my area it's usually done as young as 8 weeks). Sometimes males will not have any urges and you won't see any mating behavior until they are around an intact female. Male cats tend to know when a female cat reaches puberty before the owners do. Once she is spayed he might leave her alone. Usually yowling and trying to get to her would be because he is attracted to the hormones she is giving off. Even though he is neutered he will still have these urges and no matter how long it has been since he was fixed he will till be attracted to any female who is not spayed. Some male cats even mount spayed females after being fixed but usually the yowling stops.