My guess would be personification. When you look at the characters 老 (old) and 人 (person), it’s clearly a way to refer to an old person (not even talking about the connotation of the word).
So they refer to this processing unit as ‘old guy’, which means that it’s a fairly aged product, hence why it can’t keep up with the new, younger models.
About the connotation:
I guess it’s the ‘official’ term for an old person (or at least was so for a long time), given that the Chinese word， 老人 lǎoren for it is still exactly the same. Which, given the proper context, can make it rude in some cases because you’re using the wrong politeness level. You see it fairly often that sino-Japanese words become more complicated in terms of connotation, especially when there’s a ‘newer’ word for it which makes the old one basically obsolete.
I don’t have any resources handy right now. But as soon as I do I will add them in and update my answer need be. Just look at my answer as what I learnt from experience. Hope this helped.