Summer courses for assembling gaming PCs

Hi,
My son is 12 years old. He is interested in learning how to assemble PCs from scratch. The summer vacation in Denmark is around the corner, and he wants to spend some of his summer time assembling PCs.

Is there any place in Copenhagen or around, where he can get some hands-on experience? Of course, I can buy the hardware components for him, and he can try to assemble on his own. He has watched numerous videos on youtube and has pretty good idea how to do it. However I still prefer that he gains raw experience trying to assemble used computer components multiple times, before trying his skills on newly purchased computer components.

Any idea, where I can get fully functional old computer components?

Is there a meetup group for such child enthusiasts, where he can share and learn these kind of skills?

Regards,
Jay