They can of course be ancient or recent. They normally arise from functional
genes and not vice-versa (at least to my knowledge). They can be the result
of duplications and are then side by side on the chromosome or can be
reverse transcribed mRNA in which case they are "processed" pseudogenes and
can be virtually anywhere.
See Li and Graur "Fundamentals of Molecular Evolution" for an intro.
Regards
Paul...
