For what age of cats？

For cats 2-3 months old and in non-pregnant period.

Will cats get addicted when using catnip and gall fruit for cats frequently?

Catnip and gall fruit are natural non-toxic herbs which wont make cats addicted.However the cat balls are like reward treats and its inappropriat to overuse the catnip gall fruit balls for cat.

How will cats react to the catnip and gall fruit?

Most cats will roll on the ground,meow or even drool because catnip and gall fruit are able to release the smell much likefeline hormone making cats get high as they are in oestrus. But cats are not really in oestrus,they will recoverin 20-30 minutes

Why some cats ignore catnip or gall fruit?

Whether cats are interested in catnip or gall fruit hinges in partupon their genes. Some cats are not interested because of age. And even a fraction of cats hate catnip or gall fruit badly.