Dear Bugsy (Michael H.)
You can eat a little bit of just about anything and you shouldn't eat too much of any one thing. I guess, if I was your parents I would suggest that your brother limit his carrots just a bit, Perhaps he should swap over to apples and have something else as well.
There's probably not been a lot of research done about carrot poisoning. Drinking too much carrot juice can lead to carrot anaemia, or perhaps Vitamin A-inosis. But you'd have to eat a huge amount of carrots to get the same effect.