foo.cs

public class OldSchoolPerson {
  public string Name { get; set; }
  public int Age { get; set; }
}

public class ModernPerson {
  private string _name;
  private int _age;

  public ref string Name => ref _name;
  public ref int Age => ref _age;
}

public class C {
    public void M() {
        var oldSchool = new OldSchoolPerson { Name = "Alex", Age = 27 };
        var modern    = new ModernPerson    { Name = "Alex", Age = 13 };
        
        ModernStringMutator(ref oldSchool.Name);
        ModernStringMutator(ref modern.Name);
    }
    
    public void ModernStringMutator(ref string text) {
        text += "abc";
    }
}