C # IDataErrorInfo and child property

I have a winform related object and this object implements IDataErrorInfo. I have an error provider. The problem is changing the property of property a.

No problem when changing the age (i.e. rules are checked and displayed / removed correctly). But when I change the title of the job, the error is not displayed / removed (indeed, the Title property does not belong to the entity face). How can I complete a check?

this.errorProvider1.DataSource = this.bindingSourcePerson;
bindingSourcePerson.DataSource = new Person();
textBoxAge.DataBindings.Add("Text", bindingSourcePerson, "Age");
textBoxJobTitle.DataBindings.Add("Text", bindingSourcePerson, "CurrentJob.Title");

public class Person : IDataErrorInfo
{
    public double Age { get; set; }
    private Job _job = new Job();
    public Job CurrentJob { get { return _job; } set { _job = value; } }

    public string this[string columnName]
    {
        get
        {
            _lastError = "";
            switch (columnName)
            {
                case "Age":
                case "CurrentJob.Title":
                    if (!string.IsNullOrEmpty(CurrentJob.Title) && Age < 16)
                        _lastError = "Invalid job.";
                    break;

                default: _lastError = "";
                    break;

            }
            return _lastError;

        }
    }

    private string _lastError = "";
    public string Error
    {
        get { return _lastError; }
    }

    public class Job
    {
        public string Title { get; set; }
    }