从�生日（需要符合日期格式）得到年龄：
- (NSInteger)ageWithBirthdayString:(NSString *)birthdayString {
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:DATEFORMATTERSTRING];
NSDate *birthday = [formatter dateFromString:birthdayString];
NSDate *now = [NSDate date];
NSDateComponents* ageComponents = [[NSCalendar currentCalendar]
components:NSCalendarUnitYear
fromDate:birthday
toDate:now
options:0];
NSInteger age = [ageComponents year];
return age;
}
