Doubt about this and Arrow Function

Question

Good afternoon, I have a question about this and Arrow Function. For example:

const user = {
      age: 32,
      halfAge(){
          return this.age/2;
      },
      doubleAge: () => 2 * this.age;
    }

console.log(user.halfAge());
console.log(user.doubleAge());

Why on the console will be printed 16 and Nan? The this is variable, and when we use a Arrow Function, the this will no longer be variable and will point to the lexical context where is it? Failing to point to the global scope? or window in the browser.