This is actually somewhat common... seen once in a while, it is an
undescended testicle.  At his age, if it has not dropped, the odds are not
real good that it will.  It is just kind of a freak thing that happens and
the male still can be nuetered, although depending on where the testicle
is, the vet *might* have to open him.  I didn't catch whether there were
any breeding plans or not, and I don't know what *common* wisdom on here
is, however I will say this: I had a hob I wanted to breed who ended up
with an undescended testicles... and when I posed the question, three
different vets told me indepenantly under no uncertian terms, I should
NEVER even consider breeding him.  They said the testicle that is still
inside the body will keep the sperm at the wrong tempature and *could*
cause deformities.  At the very least, it is considered a deformity and
can be heridtary.
[Posted in FML issue 2955]