I think it's really great that you don't want your brother to feel frustrated or angry.

Children aren't just small adults. They don't process or handle things the same way AND how they do so changes all the time as they age; so what works now, might not work in a year or 2. They should come with instruction manuals!

Thanks for the game example. So, instead of something like "hey sis, can you load this game on my computer?" and "no it won't work because..." Another approach might have been to try to walk him through it. Something like... "What game?" "When did that come out" "huh, how old is the computer/what browser do you use?" "did you check if they're compatible, can they work together?" If he doesn't know what that means, how to check... then "(lets) look at the back, there's usually a spot where they list what it works with"...