一道箭头函数和普通函数的调用题，考考大家，反正我是有点晕

let kitty = {
  age: 1,
  getAge: function () {
    console.log(this.age)
  },
  growOne: function() {
    setTimeout(function(){
      console.log(++this.age)
    }, 1000)
  },
  growTwo: function() {
    setTimeout(()=>{
      console.log(++this.age)
    }, 2000)
  }
}
kitty.getAge()
kitty.growOne()
kitty.growTwo()
//输出值为啥？