Objective-C

First go the Target->Capabilities and enable HealthKit. This would setup the info.plist entry.

Make a new CocoaClass of type NSObject The filename I gave is GSHealthKitManager and the header file is as shown below

GSHealthKitManager.h

#import <Foundation/Foundation.h>
#import <HealthKit/HealthKit.h>
@interface GSHealthKitManager : NSObject

+ (GSHealthKitManager *)sharedManager;

- (void)requestAuthorization;

- (NSDate *)readBirthDate;
- (void)writeWeightSample:(double)weight;
- (NSString *)readGender;

@end

GSHealthKitManager.m

#import "GSHealthKitManager.h"
#import <HealthKit/HealthKit.h>


@interface GSHealthKitManager ()

@property (nonatomic, retain) HKHealthStore *healthStore;

@end


@implementation GSHealthKitManager

+ (GSHealthKitManager *)sharedManager {
    static dispatch_once_t pred = 0;
    static GSHealthKitManager *instance = nil;
    dispatch_once(&pred, ^{
        instance = [[GSHealthKitManager alloc] init];
        instance.healthStore = [[HKHealthStore alloc] init];
    });
    return instance;
}

- (void)requestAuthorization {
    
    if ([HKHealthStore isHealthDataAvailable] == NO) {
        // If our device doesn't support HealthKit -> return.
        return;
    }
    
    NSArray *readTypes = @[[HKObjectType characteristicTypeForIdentifier:HKCharacteristicTypeIdentifierDateOfBirth],[HKObjectType characteristicTypeForIdentifier:HKCharacteristicTypeIdentifierBiologicalSex]];
    
    
    [self.healthStore requestAuthorizationToShareTypes:nil readTypes:[NSSet setWithArray:readTypes] completion:nil];
}

- (NSDate *)readBirthDate {
    NSError *error;
    NSDate *dateOfBirth = [self.healthStore dateOfBirthWithError:&error];   // Convenience method of HKHealthStore to get date of birth directly.
    
    if (!dateOfBirth) {
        NSLog(@"Either an error occured fetching the user's age information or none has been stored yet. In your app, try to handle this gracefully.");
    }
    
    return dateOfBirth;
}

- (NSString *)readGender
{
    NSError *error;
    HKBiologicalSexObject *gen=[self.healthStore biologicalSexWithError:&error];
    if (gen.biologicalSex==HKBiologicalSexMale)
    {
        return(@"Male");
    }
    else if (gen.biologicalSex==HKBiologicalSexFemale)
    {
        return (@"Female");
    }
    else if (gen.biologicalSex==HKBiologicalSexOther)
    {
        return (@"Other");
    }
    else{
        return (@"Not Set");
    }
}



@end

Calling from ViewController

- (IBAction)pressed:(id)sender {
    
    [[GSHealthKitManager sharedManager] requestAuthorization];
    NSDate *birthDate = [[GSHealthKitManager sharedManager] readBirthDate];
        NSLog(@"birthdate %@", birthDate);
        NSLog(@"gender 2131321 %@", [[GSHealthKitManager sharedManager] readGender]);
    
    
}

Log Output

2016-10-13 14:41:39.568 random[778:26371] birthdate 1992-11-29 18:30:00 +0000
2016-10-13 14:41:39.570 random[778:26371] gender 2131321 Male