A good starting point may be a urologist.
Certainly further specialization may be in order.
Beyond age related, as you know, there are many issues to address. Stage three is livable, and not an immediate threat of death.
You are smart to take whatever steps to control the CKD possible (I was diagnose with stage 4).
I leaned "to love me blood tests," and still enjoy my life.
My hope is that you will remember , it's not the meaning of life that so important, but having meaning IN your life.
Best