Hello from JustAnswer.
I am sorry that your father has leukemia.
Advanced age certainly enters into the decision making of how to handle any cancer. Aggressive leukemia has a poor prognosis at any age. However, at an advanced age, he would be more susceptible to complications of transfusion as well as to the complications of chemotherapy. He also would be less able to tolerate aggressive treatment options, such as bone marrow transplants.
If he feels that he is a young 86 year old and would like a more extensive discussion of options, including risks involved, then it would be reasonable to seek a second opinion. And it would be reasonable for that second opinion to be obtained at a teaching/research hospital associated with a medical school. In these hospitals, there may be some newer treatment regimens being developed that may be better tolerated by someone with advanced age.
If you do not know the nearest teaching/research hospital, then if you can provide your current location, I can find the one that is nearest to you (I realize that you entered a location to register for the site, but personal information cannot be accessed by the experts to assure privacy).
If I can provide any additional information, please let me know.