public static void Main()
        {
            List <Dog> dogs = new List <Dog>()
            {
                new Dog("Sharo", 5, Gender.Male),
                new Dog("Penka", 1, Gender.Female),
                new Dog("Mara", 3, Gender.Female),
                new Dog("Ivan", 4, Gender.Male)
            };

            List <Cat> cats = new List <Cat>()
            {
                new Cat("Ivcho", 10, Gender.Male),
                new Cat("Penka", 2, Gender.Female),
                new Cat("Marian", 7, Gender.Male),
                new Cat("Ivanka", 4, Gender.Female)
            };

            List <Frog> frogs = new List <Frog>()
            {
                new Frog("Doncho", 2, Gender.Male),
                new Frog("Petko", 2, Gender.Male),
                new Frog("Albena", 3, Gender.Female),
                new Frog("Ivanka", 1, Gender.Female)
            };

            List <Kitten> kittens = new List <Kitten>()
            {
                new Kitten("Maca", 4),
                new Kitten("Penka", 3),
                new Kitten("Bojana", 4),
                new Kitten("Ivanka", 4)
            };

            List <Tomcat> tomcats = new List <Tomcat>()
            {
                new Tomcat("Pesho", 1),
                new Tomcat("Gosho", 10),
                new Tomcat("Stamat", 12),
                new Tomcat("Ivancho", 3)
            };

            Console.WriteLine("Dogs average age: {0}", Animal.CalculateAverageAge(dogs));
            Console.WriteLine("Cats average age: {0}", Animal.CalculateAverageAge(cats));
            Console.WriteLine("Frogs average age: {0}", Animal.CalculateAverageAge(frogs));
            Console.WriteLine("Kittens average age: {0}", Animal.CalculateAverageAge(kittens));
            Console.WriteLine("Tocats average age: {0}", Animal.CalculateAverageAge(tomcats));
        }