using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var list = new List<Fake>(){ new Fake(){Age = 10}, new Fake(){Age = 10}, new Fake(){Age = 20}};

        var ageCounts = from fake in list

                        group fake by fake.Age into g

                        select new {

                            Age = g.Key,

                            Count = g.Count()

        };

        foreach(var count in ageCounts){

            Console.WriteLine(count.Age +":" +count.Count);

        }                           

    }

    public class Fake{

        public int Age {get; set;}

    }

}