const Cat = (function () {
  let age = 0

  return function (name, age) {
    this.name = name
    Object.defineProperty(this, 'age', {
      configurable: false,
      get () {
        return age
      }
    })
  }
})()

let myCat = new Cat('Ivan', 10)
console.log(myCat)
console.log(myCat.name)

myCat.age = 5
console.log(myCat.age)