bald patch on my cats neck

A few days ago i noticed i bald patch on my cats neck it was not that big but i took him down to the vets and they said that there is nothing wrong with him it could be because of hes old.

but when i looked at it now its much bigger almost as long as my index finger, its not irritating him or anything but its got me worried. 

could anyone tell me whats wrong with him?

Where on his neck is it and does he wear a collar?

Its from the middle of his neck going up towards his head, no he doesn't.

Do you apply flea preventative in that spot?  I can see why you're concerned.

Does he lay by a heater? Just an odd thought I had. My old neighbors dog loved the heater and when she got older she lost her fur on the parts of her that were closest to the heater.

Couple of questions. How does his skin look? Normal, red, bumpy... Does the hair come out easily? I'm not suggesting you yank on his fur, but maybe rub the fur with your finger near the bald spot to see if any easily falls out. Also the vet said it could be age, how old is he?

no i don't apply flea preventative, i looked for fleas and he dose not have fleas.

I live in the middle east its really hot here so we don't have heaters.

thank you anyway. 

the skin looks dry but not bumpy, his hair just comes out when i touch it, it looks kinda like a knot and when i brush it it just falls out.

Hes a 9 year old Persian. 

There is a site I found that has a grid of cat ailments and the symptoms. I can't figure out how to copy links on my phone but I'll post that when I can get to a computer. I think it might help.

ok thank you very much 

http://www.peteducation.com/article.cfm?c=1+2141&aid=195

I think I got it to work! Try this link. See if anything matches. I really wouldn't think that 9 is old enough to lose hair from aging. My sister's cat lived to be over 20. Please let me know if that website helps at all.