You are not doing them any favours by leaving them entire - whether it be Male or Female - you are not taking anything away, 
in fact you are giving them a happier, healthier, 
stress free life if you neuter at 5-6 months,
prior to the hormones and adolescence kicking in, 
if you don't  nature will automatically make them want a mate. 
(or to mate!) 
Most reputable, responsible breeders will either neuter the kitten prior to leaving them, 
or insist your Pet is neutered for the sake of both of you !


Cats only Ovulate by stimulation (e.g. mating) and if left to
come into "call" (season)
and not mated, the eggs remain in the ovaries.
 With each call the unfertilised eggs will build up until they are like a bunch of grapes in the ovaries,
with the risk of cystic ovaries and
subsequently pyometra which if not treated or discovered in time will KILL.

I once had a female siamese who
did not come into "call" however over around 6 month period
 she started getting fatter and fatter, several visits to the vet who could find nothing wrong with her, 
subsequently one morning I found her dead on the floor surrounded with greenish coloured pus 
the infection that no one knew about was completely internal 
and she showed no symptoms nor signs of infection and was healthy and happy in herself - 
right up to the day the poor soul died.

A Warning to anyone considering leaving a pet female kitten or cat - un-neutered,

if you are short of money go to the Blue Cross they will help you with neutering.



Different breeds including mixed breed or the "moggy" mature at different rates, 
as a rule of thumb, 6 months is the latest time to neuter a boy, this is for his own quality of life,
 which isstopping the hormones developing.
If you have an indoor cat, do yourself and the kitten a favour and neuter by 6 months of age.
This will in the majority of cases prevent "spraying" (marking 
his territory)
Cats are the most territorial animal on the planet and eventually he will mark your home,
walls, furniture, just about everything - caused often by strangers coming to the house,
stressful situations such as annual holidays etc.,
workmen; e.g. plumbers, meter readers, decorators etc. etc.

Also of course if you allow your cat outside and he is "entire" he will travel miles to find a female, 
usually ending up dead in the road having been hit by a car.
Also of course, badly injured, caused by fighting with other males  
territory is of the utmost importance to a cat,
(they are the most territorial animal on the planet !)
and they will fight until one finally gives in
 and tries, injuries permitting, to run away.

Vet bills can run into thousands of your precious pounds.

So if you love your cat, and he is neutered he will only be allowed outside under supervision
and not left to roam, or he could be attacked by another male.

To re-iterate my comment above, if you are short of money, 
the Blue Cross will normally help you, 

especially neutering male cats.