when is it time

Question
i have a great dane (1/4 weimaraner).  he is almost 11 yrs old.  he has some cysts forming on various parts of his body and recently lost some hair on his spine toward his rear.  it looks like there might be cysts on his spine that have pushe the hair our and might open up.  he doesn't seem to be in pain but doesn't do alot but when is up and around he seems pretty normal.  i had another great dane that lived to be 12 yrs.  i think i kept him to long as the cysts opened up prior to putting him down.  when is it time.  am i doing him an injustice and being selfish by not putting him down?

Answer
I really cannot answer this question without seeing if the dog has any level of pain or discomfort. I am not a veterinarian so your best bet would be to take him to the vet and see what they have to say. They can tell you if the cysts are putting pressure on the spine and if that is causing him any discomfort. 11 years old is a GREAT age for a Dane and I am sure you have taken wonderful care of him throughout his lifetime. Whatever you decide, I wish you and your furry friend the best :)