Because there was two of us. The older computer was the second one.
Ah, I thought you were looking for old one especially, like I did earlier, before GoG, when I wanted to play old games. 
That's a decreasing truth, as the PC is being supplanted at a fast rate by tablets. The number of multi PC homes is going down, along with the sales volume in the PC market.
What you're seeing more of now is a house with one PC and then everybody having their own tablet or phone.
Yes, tablets are actively advancing, pushing laptops from "second PC" area, yet sooner or later you'll have to upgrade your old PC, and unless you're geeky and have supply of spare parts, you probably will buy second, fully assembled PC. Profit. 