PrintUserAge

static void Main()
        {
            Console.WriteLine("Enter you birthday: DD.MM.YYYY");
            string birthDay = Console.ReadLine();

            string userYear = birthDay.Substring(6, 4);
            int userYearInt = int.Parse(userYear);

            DateTime currentYear = new DateTime(DateTime.Now.Year);
            int currentYearInt = int.Parse(currentYear.ToString("yyyy"));

            int userAge = 0;
            userAge = currentYearInt - userYearInt;
            Console.WriteLine("User age is: {0}", userAge);
    }