Can I create an Android app only using Kotlin language?

Currently all I know is HTML, CSS, JS, PHP, C, and Python. I want to make android app. Should I learn Kotlin or learn Java?
If user has not updated his android os (like 4.0 icecream sandwich) will Kotlin apps work on it?
if yes then wonderful and if no, then from what version will Kotlin apps start to work?

I suggest you to learn both Java and Kotlin. Even if you won’t use Java, you’ll have to read example code from Internet, for example, or source code for Android libraries.

You can use Kotlin for 4.0, AFAIK. It compiles to the same bytecode like Java, so there’s no difference for Android, where this bytecode came from.

Yes, you can develop only with Kotlin, but as @vbezhenar says, you should learn both.

Java and Kotlin has a similar “form”, if you know one, you can learn the other quickly.