You can train your cat to use the toilet and there are actually several reasons to do it. Believe it or not, there are everything from health reasons (no dirty, germ-y litter box) to environmental reasons (clay for cat litter is strip mined).

Older cats can be trained but it's best to start when they are young. It will also depend on your cat. Cats in general don't really like change and some are more resistant to training than others. If your cat doesn't want to be toilet trained, don't push it.

If you wait until they're a few months old, that's a good time to start. They need to be big enough to jump up on the toilet and be able to balance on the bowl. I've never had a problem with a cat falling in the toilet! And they definitely will not drown in the toilet!

You do need to make sure they're still familiar with a litter box after they're toilet trained. There may be times (like if they're recovering from surgery and as they get older) when the litter box is a better option.

There are some good toilet training kits on the market. You can also get a book and find the tools you'll need on your own. Training a cat is VERY different than training a dog, so you should get a book or DVD about it at the very least.

Before you do anything, you should talk to your vet.