Alert message button, with restrictions to go further to next viewcontroller - xcode

Question

Hello I am making a ViewController with a PickerView that has age restrictions. I made it with the alert and age restrictions but I need it to deny access to next ViewController if the user isn't old enough.
Made my code like this, I guess its in the Else true I need some more code, but I'm not sure tho. I hope a kind soul can help me :)
#IBAction func verificerKnap(sender: AnyObject) {
// Creating the age restriction for the datepicker
let dateOfBirth = datoPicker.date
let today = NSDate()
let gregorian = NSCalendar(calendarIdentifier: NSCalendarIdentifierGregorian)!
let age = gregorian.components([.Year], fromDate: dateOfBirth, toDate: today, options: [])
if age.year < 18 {
// Alert controller som sender en advarsel hvis personen er under 18år
let alertController = UIAlertController(title: "Age restriction", message:
"This app requires an age of 18+", preferredStyle: UIAlertControllerStyle.Alert)
alertController.addAction(UIAlertAction(title: "Okay", style: UIAlertActionStyle.Default,handler: nil))
self.presentViewController(alertController, animated: true, completion: nil)
} else {
true

Answer 1

You can present an UIAlertController which asks if you are 18 years or older. Than link 2 buttons "Ok" and "Cancel" and add delegates for those:
let alertController = UIAlertController(title: "Default Style", message: "Are you 18 years or older?", preferredStyle: .Alert)
let cancelAction = UIAlertAction(title: "Cancel", style: .Cancel) {
(action) in
print("User is not yet >18")
}
alertController.addAction(cancelAction)
let OKAction = UIAlertAction(title: "OK", style: .Default) {
(action) in
dispatch_async(dispatch_get_main_queue(), {
self.presentViewController(desired_view_controller, animated: true, completion: nil)
})
}
alertController.addAction(OKAction)
self.presentViewController(alertController, animated: true) {
// ...
}
based on: http://nshipster.com/uialertcontroller/