I have adopted many ferrets age two or older.  The oldest two were at
least 4+ years (vet's best guess).  Other than having fewer years to
enjoy them, I see little or no difference - based on age - in the amount
of time it takes them to adjust and become loving and engaging pets.
What they went through before being rescued is probably a more critical
factor than age.  They are wonderfully adaptable - mostly they seem to
view life as one big adventure.  If ferrets could speak, I am sure their
motto would be something like "Everything was put here to play with -
and it's up to me to figure out how ..."
 
I rescued two ferrets back in 1995 that were being ignored in someone's
back yard.  A friend from work knew I was crazy about ferrets and
mentioned that the current owners didn't want them.  One was a large
beautiful female about two, the other a large undernourished, scraggly
albino male at least 4 years old.  The cage reeked (no litter pan) and
had actually rotted thru in the corner they used for poops.  I won't go
into the rest of it ... but when I got them home, they dived into the
Totally Ferret and I could hardly keep the bowls filled for a month.  And
their favorite treat was ... fresh water.  Well, the old guy had no idea
how to be a ferret - the "girls" (Sugar & Taz) and Peaches (his 2 year
old co-rescue) provided months of belly laughs as I watched them teach
Dudley how to beg for treats (and eat them), run through tubes, and even
how to dook.  Duds was gentle and quiet - went on to live to age eight -
my longest lived ferret to date.  And he never failed to thank me for a
treat - always ate it then came back to brush my foot with his chin and
look up at me a moment before trotting off ... My newest 4 year old
adoptee and his 2 year old buddy moved right in, greeted the resident
ferrets and made themselves at home, had a ball exploring and learning
the ropes.  Dooker, my all time favorite had two adrenal tumors when I
adopted him at age 11 months.  He was almost euthanized as a bad biter by
his former owner.  After surgery and a little time, he became the world's
greatest, smartest and most loving ferret (just ask me).  They were all
wonderful in wonderfully different ways.  All they needed was love, good
food, and a chance to show how wonderful they could be.  After Dooker's
death, I swore never again, couldn't take the heartache ... but I
continue to adopt, because there is nothing like a ferret.  And I never
let their age deter me - I would take a six or eight year old, as readily
as a six month old.
[Posted in FML issue 3982]