Linq, list of different objects, average()

static void Main()
    {
        try
        {
            Kitten testCat = new Kitten(10, "pesho", SexEnum.Female);
            TomCat maleCat = new TomCat(20, "misho", SexEnum.Male);
            Frog bigFrog = new Frog(50, "gabcho", SexEnum.Male);

            List<ISound> differentSounds = new List<ISound>();
            differentSounds.Add(new Kitten(10, "pesho", SexEnum.Female));
            differentSounds.Add(new TomCat(20, "misho", SexEnum.Male));
            differentSounds.Add(new Frog(50, "gabcho", SexEnum.Male));

            foreach (var item in differentSounds)
            {
                item.MakeSound();
            }

            List<Animals> differentAnimalsList = new List<Animals>();
            differentAnimalsList.Add(new Kitten(10, "pesho", SexEnum.Female));
            differentAnimalsList.Add(new TomCat(20, "misho", SexEnum.Male));
            differentAnimalsList.Add(new Frog(50, "gabcho", SexEnum.Male));
            differentAnimalsList.Add(new Frog(30, "gabcho2", SexEnum.Male));
            differentAnimalsList.Add(new Dog(25, "sharo", SexEnum.Male));
            differentAnimalsList.Add(new Kitten(5, "puhcho", SexEnum.Female));

            //one query
            var animalGroups =
                (from animal in differentAnimalsList
                 group animal by animal.GetType().Name into groups
                 select new
                 {
                     groupName = groups.Key,
                     averageSum =
                         (from anim in groups
                          select anim.Age).Average()
                 });

            foreach (var item in animalGroups)
            {
                Console.WriteLine(item);
            }
            //several queries
            Console.WriteLine("Average kitten age: ");
            var result =
                (from animal in differentAnimalsList
                 where animal.GetType() == typeof(Kitten)
                 select animal.Age).Average();
            Console.WriteLine(result);
            Console.WriteLine("Average tomcat age: ");
            result =
                (from animal in differentAnimalsList
                 where animal.GetType() == typeof(TomCat)
                 select animal.Age).Average();
            Console.WriteLine(result);
            Console.WriteLine("Average frog age: ");
            result =
                (from animal in differentAnimalsList
                 where animal.GetType() == typeof(Frog)
                 select animal.Age).Average();
            Console.WriteLine(result);
            Console.WriteLine("Average dog age: ");
            result =
                (from animal in differentAnimalsList
                 where animal.GetType() == typeof(Dog)
                 select animal.Age).Average();
            Console.WriteLine(result);


        }
        catch (ArgumentException err)
        {
            Console.WriteLine(err.Message);
        }

    }

public abstract class Animals
{
    private int age;
    private string name;
    private SexEnum sex;

    public int Age
    {
        get { return this.age; }
        private set
        {
            if (value <= 0 || value > 100)
            {
                throw new ArgumentException("Invalid age");
            }
            this.age = value;
        }
    }
    public string Name
    {
        get { return this.name; }
        private set
        {
            if (value.Length <= 2 || value.Length > 50)
            {
                throw new ArgumentException("Invalid name");
            }
            this.name = value;
        }
    }
    public SexEnum Sex
    {
        get { return this.sex; }
        private set { this.sex = value; }
    }

    protected Animals(int age, string name, SexEnum sex)
    {
        this.Age = age;
        this.Name = name;
        this.sex = sex;
    }
}

public abstract class Cat : Animals
{
    public Cat(int age, string name, SexEnum sex)
        : base(age, name, sex)
    {

    }
}

public class Dog : Animals, ISound
{
    public Dog(int age, string name, SexEnum sex)
        : base(age, name, sex)
    {

    }

    public void MakeSound()
    {
        Console.WriteLine("bau");
    }
}

public class Frog : Animals, ISound
{
    public Frog(int age, string name, SexEnum sex) : base(age, name, sex)
    {

    }

    public void MakeSound()
    {
        Console.WriteLine("gaga");
    }
}

public interface ISound
{

    void MakeSound();
}

public class Kitten : Cat, ISound
{
    public Kitten(int age, string name, SexEnum sex)
        : base(age, name, sex)
    {
        if (sex != SexEnum.Female)
        {
            throw new ArgumentException("Kittens must be female");
        }
    }

    public void MakeSound()
    {
        Console.WriteLine("miau");
    }
}

public enum SexEnum
{
    Male, Female
}

public class TomCat : Cat, ISound
{
    public TomCat(int age, string name, SexEnum sex)
        : base(age, name, sex)
    {
        if (sex != SexEnum.Male)
        {
            throw new ArgumentException("TomCats must be male");
        }
    }

    public void MakeSound()
    {
        Console.WriteLine("murr");
    }
}