Do you mean that less than 10 percent of the samples were cancer?

I believe that if a man is in his late 60s, his diagnosis is T1c,
Gleason 6=3+3, with PSA less than 10, then a small tumor volume suggests
that he may be a candidate for expectant management.  That means that
PSA will be mointored and perhaps there may be additional biopsies from
time to time.  If it appears that the cancer has started to grow more
quickly or has become more aggressive, then surgery or radiation will be
employed in an attempt to cure the cancer.  Some doctors believe that
for such men, the chances of the cancer metastasizing before anything
can be done about it are small enough that the risk is worth taking.
It is not that there is no such risk, but it has to be balanced against
the risk of adverse effects from treatment.  It is definitely true that
a significant men with prostate cancer are treated unnecessarily because
their cancers will never bother them during their lifetimes.  But it is
not possible today to decide with certainty which men fall in this
category, particularly if they are relatively young.  You may qualify
for such an approach because of the specifics of your diagnosis, and the
low tumor volume could play a role in deciding that.  But that is
something that you should decide in conjuction with your doctors, not by
asking questions on the internet and trying to figure it out yourself.
 If your doctor advises against it,  you shouldn't really try to
overrule him since you don't know as much as he does.

That refers only to microscopic evidence which could only be uncovered
if your prostate were removed in its entirety and examined by a
pathologist.  Nothing would be done about such microscopic evidence
because it hasn't risen to the level where it can be detected clinically
by current methods, including biopsy.  No physician would treat a man
who has never been diagnosed with prostate cancer on the basis that he
might have some microscopic evidence of it.

Your cancer is different.  It has grown large enough that it seems to
have affected your PSA level and it has been discovered on biopsy.  You
have joined the club of men with diagnosed cases of prostate cancer.
This club is pretty selective compared to the much larger group who have
microscopic evidence of prostate cancer.  Only one man in six is
diagnosed with prostate cancer at any time in life.

I think I summarized the situation above.  Also, both Walsh and Scardino
discuss this for men your age in their books.   But you are not going to
be able to get enough information here to make it clear what the right
decision is in your case.   You really need to rely primarily on your
doctor.  If you don't trust your doctor, get another doctor.

i don't want to overreact and

I am hardly an expert in these matters, but from what I've read, there
is no simple cutoff.  It is something that a qualified medical expert
has to approach by taking everything into consideration, and he will
take into account his knowledge of the subject and his years of clincial
experience.  As my urolgist said to me in another context, it is not
rocket scientist.   There are a lot of uncertainties and no guarantees.
  You, with your doctor guidance just have to do the best you can under
the circumstances.  I think basically you now know all the relevant
facts which can help in making the decision.  I don't think you are
going to learn much more by further testing.

Good luck.