在我的代码中，我有一个UITextField，当用户点击时会打开一个UIDatePicker，以使用户能够轻松，高效地滚动至其出生日期。显然，我们不希望UIDatePicker像当前一样向上滚动到2015年。由于这是“出生日期”输入字段，因此我还需要能够将输入限制为16岁以上。我该怎么做呢？

class SignUpViewController: UIViewController, UITextFieldDelegate {

    var datePicker:UIDatePicker!

    @IBOutlet weak var dateTextField: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()

        // UI DATE PICKER SETUP

        var customView:UIView = UIView(frame: CGRectMake(0, 100, 320, 160))
        customView.backgroundColor = UIColor.clearColor()

        datePicker = UIDatePicker(frame: CGRectMake(0, 0, 320, 160))
        datePicker.datePickerMode = UIDatePickerMode.Date

        customView.addSubview(datePicker)
        dateTextField.inputView = customView
        var doneButton:UIButton = UIButton (frame: CGRectMake(100, 100, 100, 44))
        doneButton.setTitle("Done", forState: UIControlState.Normal)
        doneButton.addTarget(self, action: "datePickerSelected", forControlEvents: UIControlEvents.TouchUpInside)
        doneButton.backgroundColor = UIColor .grayColor()
        dateTextField.inputAccessoryView = doneButton