Age verification in Objective-C

I'm creating some age-verification functionality for an iOS app. The user is presented with a UIDatePicker object, and the latest selectable date should be today minus 18 years. How vulnerable to inaccuracy is my code? How could it be leaner?

-(void)validateAge {

    NSDateComponents *today = [[NSCalendar currentCalendar] components:NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit fromDate:[NSDate date]];
    NSInteger day = [today day];
    NSInteger month = [today month];
    NSInteger year = [today year];

    int correctYear = year - 18;

    NSDateComponents *correctAge = [[NSDateComponents alloc] init];
    [correctAge setDay:day];
    [correctAge setMonth:month];
    [correctAge setYear:correctYear];

    NSCalendar *calendar = [NSCalendar autoupdatingCurrentCalendar];

    UIDatePicker *agePicker = [[UIDatePicker alloc] initWithFrame:CGRectMake(0, 240, 320, 200)];
    [agePicker setDatePickerMode:UIDatePickerModeDate];
    [agePicker setMaximumDate:[calendar dateFromComponents:correctAge]];
    [self.view addSubview:agePicker];
    return;
}

Check this method. Pass value as minus 18 (-18)

-(NSDate *)offsetYear:(int)numOfYears date:(NSDate*)date {
    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents *offsetComponents = [[NSDateComponents alloc] init];
    [offsetComponents setYear:numOfYears];

    return [gregorian dateByAddingComponents:offsetComponents
                                  toDate:date options:0];
}

StackExchange Code Review Q#16145, answer score: 2