error: synthesized property 'name' must either be named the same as a compatible instance variable o

#import <Foundation/Foundation.h>

@interface Person : NSObject{
    NSString * _name;
    NSUInteger _age;
}

@property (nonatomic, copy) NSString* name;
@property (nonatomic, assign) NSUInteger age;

@end

@implementation Person

@synthesize name = _name;
@synthesize age = _age;

@end

正确实现如上述代码，以前参照Object-C程序设计 （第4版）写的实例，就是报：

error: synthesized property 'name' must either be named the same as a compatible instance variable or must explicitly name an  instance variable错误。

参考书中改代码以下：

#import <Foundation/Foundation.h>

@interface Person : NSObject

@property (nonatomic, copy) NSString* name;
@property (nonatomic, assign) NSUInteger age;

@end