using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public class Person 

    {

        public string Name;

        public int Age;

        public string Sex;

    };

​

    public static void Main()

    {

        List<Person> PerList = new List<Person>(){

                new Person(){ Name = "Sam", Age = 50, Sex = "Man" },

                new Person(){ Name = "Amy", Age = 30, Sex = "Woman"},

                new Person(){ Name = "Andy", Age = 30, Sex = "Man"},

                new Person(){ Name = "Jacky", Age = 60, Sex = "Man"},

                new Person(){ Name = "Peter", Age = 65, Sex = "Man"},

                new Person(){ Name = "Susan", Age = 45, Sex = "Woman"},

                new Person(){ Name = "Jeff", Age = 65, Sex = "Man"},

                new Person(){ Name = "Mary", Age = 63, Sex = "Woman" }};

        var peopleAgeTop3 =  PerList.GroupBy(p => p.Age)

                                    .OrderByDescending(g => g.Key)  // key is age

                                    .Take(3)

                                    .SelectMany(g => g);

        foreach(var p in peopleAgeTop3)

            Console.WriteLine(p.Name);

    }

}