I neutered my male before the female got her first heat and I am waiting until she is one and a half to spay her (bigger organs, less complications in surgery...). I wonder if there is a way to raise his interest and if it would calm her down.
Firstly, I don't think there is a way to raise his testosterone in a safe way. Once he's neutered, he's neutered. Secondly, this would not be advised as there's no saying that she would pick him as a mate anyway. In fact, she probably wouldn't since he would have lowered testosterone levels and the female cat will only mate with a male that is "desirable" that she thinks would produce good offspring. Lower levels of testosterone would pretty much eliminate him as a contender.So it probably would not calm her down. Lastly, once your female has had her first heat, it is considered safe to get her spayed anyway. In fact, it is considered safe even before that but once she's had her first heat, you know for sure that it's safe to spay her. So if you get her spayed now, you won't have to worry about that anymore anyway. And you definitely should get her spayed now because some cats when they're in heat will do everything they can to get out of the house and find a mate and then you'll end up with a bunch of unplanned kittens!
Over the decades, we have spayed 9 females when they were about six months old, with no complications. There is no need to wait until the cat is 1.5 years old. Cats who are spayed before first heat are less likely to get breast cancer, and of course, will not have kittens.
As for feeling guilty about neutering your male cat before he had "done the deed", wouldn't he be more likely to miss what he knew rather than what he had never known? Is your cat happy? If so, you have nothing to feel guilty about.
Whether or not there is a way to do so, it would serve no purpose whatsoever.
Sex for cats is 100% about reproduction, nothing more. The drive to mate is instinctive it has nothing to do with pleasure. A neutered male does not miss sex or yearn for it. After the removal of their testicles, drastically reducing the amount of testosterone in their system, they pretty lose any tendency to act like an un-neutered male.
Did you know that for the female cat, intercourse is quite painful? A male cat's penis is radically different than a human males and it has backward pointing spikes on it which cause pain for the female when, he withdraws.
It is fairly widely agreed that the pain is what triggers the ovulation in the female - cats do not ovulate and then wait to get pregnant. A female cat will only ovulate after mating.
Just for the record, female cats do not have menstrual cycles like human female. I believe that human females are the only species which has such cycles,
Don't worry that your neutered cat is missing out on something special - he isn't.
EDIT - I should have added that waiting for a female to be one and half years old is far too long before spaying her. While it is possible to neuter a male too soon, it is actually rather hard to spay a female to early, but it can be done. The size of the organs have no bearing on the surgery except that the smaller the ovaries and uterus, the small the incision need to remove them.
A year and a half is way longer than you should wait. Call a vet office and ask them the age they recommend. It should not cost anything to get such an answer.
If you want to see what the surgery entails, go what the video at https://www.youtube.com/watch?v=7YKC7fQT1zE It isn't a bloody video or such and it is quite interesting to watch just what is done.