Why are properties required in C#

public class Test

    {

       private int age = 0;

       public int Age

       {

           set { age = value; }//assign user input value in age variable

           get { return age; }//getting age variable value

       }

    }

And in another class we can access properies to assign and get values

public class Demo

   {

       Test objTest = new Test();

       //assign value to property and variable

       public void SetValue()

       {          

           objTest.Age = 12;

       }

       //get value to property and variable

       public void getValue()

       {

           System.Diagnostics.Debug.WriteLine(objTest.Age);

       }

   }

But I can do same thing with public variable so why use properties?

because we can add condition on input value in set block and can add addition on output value in get block

for example condition on input value

public class Test

    {

       private int age = 0;

       public int Age

       {

           //assign user input value in age variable

           set

           {

               if (value >= 18)

               {

                   age = value;

               }

               else

               {

                   age = 0;

               }

           }

           get { return age; }//getting age variable value

       }