I used to have this kind of situation before. My youngest sister always wanted whatever I have like if I have something like this, she'll ask our parents to bought the exact same thing. She also wanted to try everything that I tried which made me really pissed off. Over time, I just didn't give a damn anymore and just reminded her that you should not copy whatever I have and especially that you just want them and you don't need them. Now, we are the closest in our family and she graduallly understood to live her own life.

I suggest for you to not give him the unnecessary attention that he needed and talk to him calmly on how bad and annoying the way he copied your moves even though you know that he is just really curious.

I think it all comes down on how they execute their curiousity? Like if they are curious and humble, you would gladly help and teach hi, but if he is curious and intended to annoy you, you will really going to be pissed off.