Guinea pig or another rabbit, if he's young he could take a rat dieing so soon very hard since he's still growing up plus guinea pig's & rabbits live long up to 30 if cared for properly and as Alicia has said they have to be nutured/spayed if you want them to live that long and healthy of course.

My favourit breed of guinea pigs is the Abyssinian, they have awsome fur and there SO adorable .. the pure black one's are the best for me they look like punks lol, there easy pets to take care of and are very smart.

Again it's up to your brother, if he knows how long a rat will live compared to a guinea pig then let him choose, I'm sure he knows what he'll want.

Here is a cute breed of guinea pig.



He could even get a bird there great pets and simple to take care of, budgies are the most commen .. it's good to get them young this way there tame, if you have any questions on birds shoot at me I have owned birds all my life.