Rats make great pets for children and adults, but you always should be educated about them. A common misconception people have is whenever they think of a pet rat, they think of the misunderstood classroom pet, a rat in a rectangular wire cage or glass aquarium, with a wire wheel, sawdust bedding, and a plastic water bottle and food bowl. A true rat owner knows better than to keep an energetic animal in such a cruel habitat.
A single rat could get very depressed and lethargic, possibly even aggressive without a friend or two. And really, people give excuses like, "Well, rats are too expensive," or, "It'll be too hard to care for more rats and it'll be smelly!" Anyone who's been to the average pet store knows a rat only costs $6-10 for one rat! Rats adopted from adoption centers cost slightly more, but for a healthy, happy pet rat, you would probably want the best for him. Plus, rats don't have any smelly odors unless you fail to clean his enclosure or cage once a week, and they are very easy to care for.
Female rats are especially energetic, and a lack of companionship (especially if she had been living with other rats when she was still at the pet store) can be fatal.
In general, all single rats experience loneliness just as a human does, and even if the cage is when a lot of human activity is, and you let him out every day, he still won't have interaction 24/7.
For example, you won't be playing or interacting with your rat when you're at work or doing errands. Your rat will have someone to snuggle with during all those times he's in his cage during those long hours you are away from the house.
Rats are "pack" animals, and they love to be in groups of their own kind. Your rat could not only get sick and depressed without any rat friends, he could also be fearful and angry towards you. Rats don't generally bite, but a rat in a small cage with no rat companions could get upset enough to produce a small nip. A single rat gets over-protective over his sleeping house, toys, and other things you may not know he is protecting until he defends his cage and territory. Many people that have had rats for several years only keep one rat with success, but if you're a first-time rat owner, then you need to learn the facts. You should really get two, three, or even four rats instead of just one, not only for the pleasure of rat companionship for a great experience when you have them as pets, but for the rats to be truly happy with their friends and live their lives to the fullest!