Hi I have a five year old Tom cat he has always been very clingy and insecure since he was a kitten. He is very timid and scared of his own shadow. He doesn't like going outdoors. He is an indoor cat. I am out at work every day so I have been considering the idea of getting a kitten to keep him company but I don't want to cause the older cat stress. Is it a good idea or a bad one?:)

If I got one it would be a female.
There are many ways you could try this,
1 being that you could get one from a rescue and see if they would be willing to take it back if things did not work out.
2 you could foster a kitten yourself and see what happens maybe you could end up adopting it.

Remember that it will probably take him some time to get used to it. You could not just put them together and expect them to bond right away.
My older cat could careless if he had other animals around and it took him many months to get used to me bringing them in. But he is the exact opposite of yours, he enjoys the outdoors and is not afraid of anything. I think having other cats in my home has helped him... he is not as mean as he used to be.
It may just be the thing your cat needs to bring him out of his shell. Good Luck with your choice.

Is the cat clingy, or is he possessive? If he's five and has been used to having you all to himself, he is unlikely, in my opinion, to accept sharing you with another cat. You may wind up with a truce, where both cats coexist, but I don't know if I would expect them to be friends.

However, all cats are individuals, and it's hard to predict what they will do until you try. You probably would be better off going with an adult cat (I'd suggest the 1-2 year old range), with a nice, mellow, laid-back personality. A kitten is probably going to be to pesky, and the last thing you want is to bring in another clingy cat, or an aggressive one, and that's easier to tell with an adult than a kitten.