12 year old cat with butt dandruff

My 12 year old cat has a lot of dandruff on his back and butt, everytime I try to comb it out he sort of freaks out (probably because it itches or feels weird)

He has no scabs or bites, no fleas but lots of dandruff. I have used an organic oatmeal dandruff spray on his back and spots, is there anything else I can do to make this better for him? How can I fix this?

Also there is no hair loss

Of course, the first response should probably be, "Have you asked your veterinarian?"    

That aside, what food is he on?  Sometimes skin problems can be caused by allergies, and other times a switch in diet - to promote the health of the follicles and sebaceous glands -  can do wonders for the skin and coat.  

He's not grooming that area, possibly getting some arthritis or is overweight and it's not easy to reach.

This is a common cause of dandruff.

There are also medical reasons too that are possible.

Diabetes, hyperthyroidism to name a couple that will cause dandruff.

Also if his food is too low in fat.

I would think about getting him a senior wellness checkup soon, just to be sure things are good inside where we  can't see, but can see an effect such as dandruff, and you won't want to find out by his getting sick.

I agree with all the other posts. It is normal for a cat to react to you scratching the base of the tail either they'll try to nip at you to get you to stop because they hate it or they'll start bobbing their head head up and down reacting similar to a dog being scratch just in the right place on its tummy.

First, trip to the vet for a thorough check up with senior panel bloodwork.  Then, what kind of food are you feeding?  If you're feeding dry, try adding some wet food to your kitty's diet.  You could also look into an omega-3 supplement such as Wellactin.