Why doesn't my code work?

Question

fun main(args: Array<String>) {
var age = readLine()!!.toInt()
var result = when {
age <= 11 -> "Child"
age == 12 && age <= 17 -> "Teen"
age == 18 && age <= 64 -> "Adult"
age => 65 -> "Senior"
age < 0 -> "Invalid age"
}
println(result)
}

The result is: error

Answer 1

If you try to run the code in the code playground, you can also look at the full error message.
A when expression must be exhaustive. If the cases are not enums, you need an 'else' branch at the end.
Mind the order of your conditions. If you write <=11 first, then <0 at the end will never be evaluated, because negative numbers have already satisfied <=11.
=> is not a proper comparison operator.
And finally a number cannot be equal to 12 AND smaller or equal to 17 at the same time, unless it's exactly 12.

Answer 2

Lisa Tibor Santa Thanks!

Answer 3

For example, look at the 2nd condition:

age == 12 && age <= 17 is only true when age = 12.

You probably mean
age >= 12 && age <= 17

Same thing in the 3rd condition.