Objective c simple sorting using NSSortDescriptor - xcode

Question

I want to simple sorting in nslog , this is my viewcontroller.
- (void)viewDidLoad {
[super viewDidLoad];
sobj=[[SortObjects alloc]init];
sobj.description; //this doesn't work
[sobj description];//this doesn't work either
NSLog(#"sobj = %#", sobj);
}`
& here is my Object Class SortObjects.h
enter code here- (NSString *)description {
return [NSString stringWithFormat:#"%# %#", self.firstName, self.lastName];
NSArray *firstNames = #[ #"Alice", #"Bob", #"Charlie", #"Quentin" ];
NSArray *lastNames = #[ #"Smith", #"Jones", #"Smith", #"Alberts" ];
NSArray *ages = #[ #24, #27, #33, #31 ];
NSMutableArray *people = [NSMutableArray array];
[firstNames enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
SortObjects *sObjects = [[SortObjects alloc] init];
sObjects.firstName = [firstNames objectAtIndex:idx];
sObjects.lastName = [lastNames objectAtIndex:idx];
sObjects.age = [ages objectAtIndex:idx];
[people addObject:sObjects];
}];
NSSortDescriptor *firstNameSortDescriptor = [NSSortDescriptor sortDescriptorWithKey:#"firstName"
ascending:YES
selector:#selector(localizedStandardCompare:)];
NSSortDescriptor *lastNameSortDescriptor = [NSSortDescriptor sortDescriptorWithKey:#"lastName"
ascending:YES
selector:#selector(localizedStandardCompare:)];
NSSortDescriptor *ageSortDescriptor = [NSSortDescriptor sortDescriptorWithKey:#"age"
ascending:NO];
NSLog(#"By age: %#", [people sortedArrayUsingDescriptors:#[ageSortDescriptor]]);
value of sobj is coming null in nslog??