userID

using System;
using System.Linq;
namespace LetYouGo
{
    class LetYouGo
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Enter your ID (ID must be a 10 digit number): ");
            string id = Console.ReadLine();

            //validate user id

            if (id.Length != 10)
            {
                Console.WriteLine("Invalid ID!");
            }
            else
            {
                Console.WriteLine("Valid ID");
            }

            //define user gender


            string gender = id.Substring(8, 1);

            int genderChecked = int.Parse(gender);
            if (genderChecked % 2 == 0)
            {
                Console.WriteLine("Gender: Male");
            }
            else
            {
                Console.WriteLine("Gender: Female");
            }

            //define user age

            string yearOfBirth = id.Substring(0, 2);

            int year = int.Parse(yearOfBirth);
            string MonthChecked = id.Substring(2, 2);
            int MonthResult = int.Parse(MonthChecked);
            if (MonthResult >= 21 && MonthResult <= 32)
            {
                year += 1800;
            }
            else if (MonthResult >+ 41 && MonthResult <+ 52)
            {
                year += 2000;
            }
            else
            {
                year += 1900;
            }

            Console.WriteLine("Year of birth: " + year);

            string dayOfBirth = id.Substring(4, 2);
            string monthOfBirth = id.Substring(2, 2);

            //days left till next birthday

            int day = int.Parse(dayOfBirth);
            int month = int.Parse(monthOfBirth);
            int userAge = 0;
            userAge = DateTime.Now.Year - year;
            Console.WriteLine("User age: " + userAge);


            //write user birthday on the console

            if (year >= 2000)
            {
                month = month - 40;
            }
            if (year <= 1900)
            {
                month = month - 20;
            }


            Console.WriteLine("User birthday: {0}.{1}.{2}", dayOfBirth, month, year);

            DateTime futureDate = new DateTime(DateTime.Now.Year, month, day);

            Console.WriteLine("Next birthday: {0:dd/MM/yyyy}", futureDate);

            DateTime currentDate = new DateTime();
            currentDate = DateTime.Now;

            TimeSpan days = futureDate.Date - currentDate.Date;
            int daysLeft = (int)days.TotalDays;
            Console.WriteLine("Days left till next user birthday: {0}", daysLeft);
        }
    }
}