how to set 'setter' of an computed property to private?

I know how to set 'setter' of an stored property to private (e.g. public private(set) var name: String = "John") but how do we set 'setter' of an computed property to private? In this case the 'setter' for the variable 'age'. When I tried to put an keyword private in front of set(newAge){}, XCode display an error. So is it possible to set 'setter' of an computed property to private?

public class Person {

    public private(set) var name: String = "John"

    var age: Int{
        get {
            return 10
        }
        set(newAge){ // how to set this setter to private so to restrict modification

        }
    }
}