Is this age-related decline in GFR or kidney disease?

Wow! Thank you for that reply.
I totally agree that it is unfortunate that they call it chronic kidney disease. Stage 3. It makes it sound like you are going to die tomorrow. No one mentioned it until October of this year.
My dr said I don't drink enough water so I am now drinking 24 ounces per day and I have stopped taking aspirin or other NSAIDs. I go back at the end of January to retest.
You are awesome so keep up the good work

Windyshores:
I may have mentioned that my Dr said that GFR naturally declines with age in many (not all) people. This does not mean you have Disease. This is backed up in many medical journals. So, we will see.

Anytime you are hesitant to accept your doctor's diagnosis, get a second opinion from another specialist !!! Your peace of mind is a big factor in being well. I have sometimes taken the words of a nurse more seriously, they have seen everything and trained in all areas somewhere along the line. I have Sjogren's disease and would not have seen a rhuematologist had it not been for a nurse's kind words to me after my doctor's appt. It won't offend the doctor, they see this all the time, lots of patients get frustrated with an illness and your kidney's are extremely important. Just do it tomorrow, and good luck! All the above may contain advice, but think of your peace of mind and go get it eased. It may be extremely important either way.

I’ve been watching this discussion for a while now. A bit of background first: I have 50ish years of diabetes and a history of hypertension. I have an endocrinologist for the diabetes (also a history of hyperthyroidism). In 2005 I had a pancreas transplant and found out that I also had mild to moderate kidney function trouble. There were no stage or alphabet numbers in the diagnosis and a simultaneous kidney transplant was not recommended at that time. I was 48 at the time.
In 2008 I started seeing a nephrologist and started learning about chronic kidney disease. I learned about controlling hypertension, eating and hydration for kidney disease and tests such as creatinine, BUN, Cystatin-C, and eGFR. From 2016 to now my eGFR has bounced between 14 - 42. It is currently in the low 30’s (34 I think). My nephrologist labeled me as CKD stage 4. He says that dialysis &/or transplant are in my future. So I’ve learned as much as I can about kidney transplantation and living kidney donation. I have gone through kidney pre-transplant evaluation and have been approved & accepted for kidney transplant when that time comes. It isn’t considered until the eGFR is less than or equal to 20. (I am not a fan of dialysis; but I’ve learned about that too.)
I’m nearly 68 now and doing well. I see the endocrinologist & the nephrologist every 3 months (or their physician’s assistants alternating). I also gets labs done about a week before these appointments. My primary, endocrinologist and nephrologist are all in the same health care system so it is easy for record sharing and to make sure we’re all on the same page. These providers are great and they each have their purposes. I’ve learned not to rely on the primary internal med Doc for diabetes and CKD advice because that is what the specialists are for.
One last thing. I’ve had kidney biopsies. It was part of a research program having to do with my pancreas transplant. It was NOT fun. I would not recommend it unless there is a very compelling reason for it. Not sure that an ultrasound etc. is all that useful for diagnosing CKD unless there is some other kidney condition that warrants it.

Well- all I did was to completely change my life in terms of what I was eating. I've always been into exercise so I just kept doing that and even increased it a bit by taking up the sport of fencing. I also left the nephrologist I was seeing who wanted me to immediately get a fistula and found one who was willing to work with me to stay off dialysis.