Try... kindergarten, when I decide that "children" is a dirty word because the way the teachers always use it to address their involuntary subordinates.
Or age 13 when I'm trying to have serious debates with adults since I'm *bored out of my skull* with popularity-seeking peers.
Heck, I even joined a "child rights" group that ended up being about --surprise!-- grandparents wanting better access to custody (aka ownership) of their grandkids. Screw that.
Well, I'm 21 now and I haven't forgotten. Personally, I think that this group, and the movement it could potentially represent, might be far stronger if partnered with the *other* end of ageism, that-- while of course different-- has a lot to learn and offer us.
And btw, "you're just a kid" doesn't end when you hit the age of majority. gr.