The NSDate extension for calculating the age.

NSDate+Age.h

//
//  NSDate+Age.h
//
//  Created by Daniel Hsieh on 2018/7/6.
//

#import <Foundation/Foundation.h>

@interface NSDate (Age)

- (NSInteger)age;

@end

NSDate+Age.m

//
//  NSDate+Age.m
//
//  Created by Daniel Hsieh on 2018/7/6.
//

#import "NSDate+Age.h"

@implementation NSDate (Age)

- (NSInteger)age {
    return [[NSCalendar currentCalendar] components:NSCalendarUnitYear
                                           fromDate:self
                                             toDate:[NSDate date]
                                            options:0].year;
}

@end