public class People
  {
    public string name { get; set; }
    public int age { get; set; }
    public string sex { get; set; }
  }

  List<People> peoples = new List<People>()
      {
        new People() {age = 11, name="alun", sex = "男"},
        new People() {age=25, name = "陈敬桃", sex = "男"},
        new People() {age=9, name = "惠安", sex = "男"},
        new People() {age = 45, name = "小票", sex = "女"},
        new People() {age=3, name = "晓鸥", sex = "女"},
        new People() {age=70, name = "望谟", sex = "男"}
      };

 public class PeopleAgeComparer : IComparer<People>
  {
    public int Compare(People p1, People p2)
    {
      return p1.age.CompareTo(p2.age);
    }
  }

peoples.Sort(new PeopleAgeComparer());