Catnip making kittens aggressive?

From what I've read online kittens cannot be affected by catnip until they are around 3 months. Why is it making my usually sweet tabby fosters aggressive? They're 7.5 weeks old. I've had them since they were 5 days. The catnip toys make 3 of the 4 VERY aggressive and possessive. Anyone experienced this before? I thought I'd post here instead of in behaviors because I figured there'd be more kitten experienced people here. I've since removed said catnip toys from their room and the behavior has stopped.

I guess I should add that I took the two toys away and the behavior stopped and then I put them back to test it and they became aggressive again. It is indeed the toys. Of all the fosters I've had, and there have been a fair few, I've never experienced this before and am at a los. Is this any predictor of their adult personalities?