Hi,
It's difficult enough to get 1 Hermanni Hermanni (believe me!) so where will you get 2?
I don't think they get lonely, but I think having more than 1 provides stimulation. That is only my opinion, and Alan is right - sometimes you find out that it is impossible to keep two together and then you are faced with having to rehome one or set up another enclosure. As for the age, most breeders sell that under 1 years old.
Hope this helps!