I too find that using real life similes is very efficient for explaining computers to older people. For example my favorite simile to use is to explain how a computer works, typically so an older person can understand why they need more memory for their computer, not a faster processor or bigger hard drive. The illustration goes like this:

A computer is like a person studying at a library. The CPU is a person reading books. The RAM is a table at which they are sitting with their books spread out. The library shelves are the hard drive. The books in the library are their programs and documents.

Using this illustration I then explain swapping to them. Imagine if a person is doing some serious studying and needs to have 20 books open at once to read but their table is only big enough to hold 10 books. As a result they have to get up and put books back on the library shelf, move other books off the shelf onto the table, then put those books back on the shelf to get the first books back off the shelf and onto the table. This slows down the person's studying a lot.

I use this illustration to explain why you need more memory (table space) if your computer is swapping, and why you don't need a new hard drive (shelf space).

This same illustration works for other things as well: A dual core processor is two people reading at the same table. You need a bigger table if you want both people to be able to use the table affectively. If the computer is running out of hard drive space it is like the library shelves are full.

This basic illustration explains a lot about computers in a brief period of time, and I've had numerous people who don't understand how their computer works praise me for it, and say that now they really feel like they understand what is going on.

I like finding simple explanations for complicated things.