Properties private set;

This is one possible solution although not very clean:

1. Make the property you need to expose to BAL & DAL internal
2. Mark BAL.dll & DAL.dll Internal Visible in assemblyinfo.cs

public class Person
{
    public Person(int id)
    {
         this.Id=id;
    }

    public string Name { get;  set; }
    public int Id { get; internal set; }
    public int Age { get; set; }
}

AssemblyInfo.cs for Entities.dll

[assembly: InternalsVisibleTo("DAL"), InternalsVisibleTo("BAL")]

That way all your internals will be visible to DAL & BAL. This may not be desirable but I'm just suggesting one possible solution.

The two common approaches are either that the class should have a constructor for the DAL to use, or the DAL should use reflection to hydrate objects.

Or you can do

public class Person
{
    public Person(int id)
    {
         this.Id=id;
    }

    public string Name { get;  set; }
    public int Id { get; private set; }
    public int Age { get; set; }
}