I think today the only prerequisite would be to be able to generally use a computer. I'd say if you spend any hours a week on facebook, you can probably figure out how to use bitcoin. That said I wouldnt recommend someone who isn't fairly technically competent to out much money into bitcoin. Right now it's too easy for the average joe to get scammed or lose his bitcoin.
If one thinks that they can get infected by a computer virus, don't expect them to be able to understand bitcoin.