New kitten keeps eating resident cat's food

Hi reddit, I'm looking for suggestions on how to stop my new kitten from eating our resident cat's food.

Resident cat is around 4 years old and we have had her for around that many years. We got a kitten a few weeks ago (we have acclimated them and they are fine together now, no issues with them together other than he annoys her sometimes). The concern I have is their food.

Since he's only a few months old he is kn kitten kibble, the same one he was on at the shelter. Resident cat is on adult kibble and wet food. He eats all his food instantly while she (resident cat) grazes (she eats all her wet food but grazes her kibble). Because she leaves her kibble there, he has tried to eat it. Not only do we not want him eating adult cat kibble, we also want to make sure she has food to come back to.

At the moment we have resorted to putting her food on one of our desks, but obviously this is not viable long term. When it's time to feed them, she is waiting in the lounge room where we put his food because she used to eat there, and we have to keep showing her where her food currently is. But also, eventually he will be able to jump onto the desk and eat her food.

I'm looking for suggestions on how to stop him from eating her food. Will he grow out of it? We have considered getting a microchip feeder for resident cat, but they're expensive for our budget (we would be able to make it work if it's our only option). If he will grow out of it, then are there any suggestions for things we can do in the mean time? Or do we need a permanent solution?

If it's relevant, I live in Australia.

Thanks everyone!