No age risks with catnip. However, most kittens don't really become receptive to the effects of catnip until they're a little older. My 2 didn't react to it until they were about 4 1/2 months, but it varies with each cat. Try it and see!
"To close your eyes will not ease another's pain." ~ Chinese Proverb
“We must not refuse to see with our eyes what they must endure with their bodies.” ~ Gretchen Wyler