在线等...求教高手补全下面的程序

Question

在班级类中增加一个能计算班级平均年龄的方法，每个班输入第一个学生学号，其它学号自动生成，如01班第一个学生学号为09010101，则其它学生的学号依次为09010102~09010105。在主程序Main中建立3个班，每个班5个学生，读入相关数据，输出每个班及学生的有关信息和该班学生的平均年龄。下面是我写的程序，请高手为我补全赐教，要具体的程序代码
using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;namespace ConsoleApplication1
{
    class Student
    {
        private string ID;
        private string Name;
        private string Sfzh;
        private char Sex;
        public string id
        {
            get
            {
                return ID;
            }
        }
        public string name
        {
            get
            {
                return Name;
            }
            set
            {
                Name = value;
            }
        }
        public string sfzh
        {
            get
            {
                return Sfzh;
            }
        }
        public int age
        {
            get
            {                int age = DateTime.Now.Year - int.Parse(Sfzh.Substring(6, 4));
                return age;
            }
            set
            {
                age = value;
            }
        }
        public char sex
        {
            get
            {
                return Sex;
            }
            set
            {
                Sex = value;
            }
        }
        public Student(string name, string id, char sex,string sfzh)
        {
            Name = name;
            ID = id;
            Sex = sex;
            Sfzh = sfzh;
        }
        public void Display()
        {
            Console.WriteLine("姓名{0}，学号{1}，性别{2},年龄{3}", Name, ID, Sex,age);
        }
    }
    class Class
    {
        private string cID;
        private string counsellor;   //辅导员
        private ArrayList stu;       //学生数组
        public string cid
        {
            get
            {
                return cID;
            }
        }
        public string cname
        {
            get
            {
                return counsellor;
            }
            set
            {
                counsellor = value;
            }
        }
        public Class(string cid, string cname)
        {
            cID = cid;
            counsellor = cname;
        }
        public void CreateClass()
        {
            stu = new ArrayList();
            string name, id,sfzh;
            char sex;            
            for (int i = 0; i < 5; i++)
            {
                Console.WriteLine("请输入第{0}个学生的信息：", i + 1);
                Console.WriteLine("姓名：");
                name = Console.ReadLine();
                Console.WriteLine("学号：");
                id = Console.ReadLine();
                Console.WriteLine("性别：");
                sex = char.Parse(Console.ReadLine());
                Console.WriteLine("身份证号：");
                sfzh = Console.ReadLine();
                stu.Add(new Student(name, id, sex,sfzh));
            }
        }
        public void Display()
        {
            Console.WriteLine("班号{0}，辅导员{1}", cID, counsellor);
            IEnumerator ie = stu.GetEnumerator();
            while (ie.MoveNext())
            
                ((Student)ie.Current).Display();  
            }
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            string cid, counsellor;
            Console.WriteLine("请输入班号：");
            cid = Console.ReadLine();
            Console.WriteLine("请输入辅导员姓名：");
            counsellor = Console.ReadLine();
            Class s = new Class(cid, counsellor);
            s.CreateClass();
            s.Display();
        }
    }
}上面的程序应该具体怎么改，才能达到我想要的结果，求教啊，急！！！