Toddler overly concerned about baby.?

Though it may be annoying, I think his concern for his brother is great. Way better than the opposite end of the spectrum where the older sibling resents his younger sibling and develops jealousy and rivalry. He takes his role as big brother very seriously and isn't willing to let his brother suffer any injustice-- no matter how tiny this perceived 'injustice' is! That may really be helpful when they are both older and he is willing to protect and stick up for his little bro.