Installing android 9 or 10 on iphone 4

Is it possible to install Android on an iPhone 4?

Technically speaking, yes. The bootrom of the iPhone 4 has long been exploited. If you want to try, here's a few steps you can take:

1. Exploit your iPhone 4 using any bootrom exploit
2. Build a custom Android kernel for your iPhone 4
3. Write a custom loader with all the necessary configuration and components
4. Boot it on the iPhone 4

What're the missed requirements?

There could be a lot of them, for example, the storage chip, the CPU, a lot of things can go wrong with this type of exploit.

What's the latest version that can run on the iPhone 4?

None. But if you somehow manage to get Android running on it, I would say you can run up to Nougat. Because your iPhone 4 have a single core and 512mb of ram, this configuration is similar to another device called Samsung Galaxy Star and it has almost the same configuration in terms of ram and CPU cores, and it is able to run up to Nougat.