         return rx
     }()
     
-    private let maxCreditCardAge = 21
-    
     private var month: Int?
     private var year: Int?
     

import UIKit

public class CardExpiryDateTextField: OmiseTextField {
    private let expirationRx = { () -> NSRegularExpression in
        let options = NSRegularExpressionOptions(rawValue: 0)
        guard let rx = try? NSRegularExpression(pattern: "^(\\d{1,2})/(\\d{1,2})$", options: options) else {

        let text = self.text ?? ""
        let range = NSRange(location: 0, length: text.characters.count)
        let options = NSMatchingOptions(rawValue: 0)
        guard let match = expirationRx.firstMatchInString(text, options: options, range: range) where match.numberOfRanges >= 3 else {
            month = nil
            year = nil
            return
