C#Linq语句与List结合使用

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication6
{
    public class Student
    {
        private int ID;
        private string name;
        private int age;
        public Student(int id, string _name,int _age)
        {
            ID = id;
            name = _name;
            age = _age;
        }
        public int _ID
        {
            get
            {
                return ID;
            }
            set
            {
                ID = value;
            }
        }

        public string Name
        {
            get
            {
                return name;
            }
            set
            {
                name = value;
            }
        }
        public int Age
        {
            get
            {
                return age;
            }
            set
            {
                age = value;
            }
        }
    }

    public class StudenManager
    {
        public List<Student> sm = new List<Student>();
        public void Attach(Student s)
        {
            sm.Add(s);
        }

        public void IDOutPut()
        {
            Console.WriteLine(sm.OrderByDescending(item => item.Age).Last()._ID);
        }

        public void AgeOutPut(int age)
        {
            Console.WriteLine(sm.Find(item => item.Age == age).Age);
        }

    }
    class Program
    {
        static void Main(string[] args)
        {
            Student s1 = new Student(1,"xiaoming",18);
            Student s2 = new Student(2, "xiaowang", 15);
            Student s3 = new Student(3, "xiaoli", 16);

            StudenManager sma = new StudenManager();
            sma.Attach(s1);
            sma.Attach(s2);
            sma.Attach(s3);

            sma.IDOutPut();
            sma.AgeOutPut(s1.Age);
        }
    }
}