Refurbished computers can go either way in my opinion. If it comes with a warranty in case something goes wrong, which is usually the case, I wouldn't worry too much about it. Often, refurbished computers are just returned by the user due to dissatisfaction or maybe something was wrong before it was refurbed. It doesn't necessarily mean it was used for years already. It might only have been used a few days.
My father has purchased several refurbished laptops which were older and probably used for quite some time. He has NOT had good luck with this. Due to the sensitive nature of the inside of a laptop, they just don't seem to last as long as a desktop. The refurbished laptops always die on him within a couple years.