The life expectancy of someone with COPD will depend on how far advanced the COPD is.
If the COPD is very severe and you don't get treatment for the COPD the person could die within a year or two after being diagnosed.
In some cases treatment does help but if the COPD is too severe then you still might die even with treatment.
If you're smoking and are diagnosed with COPD then you need to stop smoking right away to help your lungs heal and increase your chances of survival.
My Grandma died at the age of 68 from COPD and smoking. She was diagnosed a year before that and then wound up in the hospital and died within a few weeks of being in the hospital.
So she only lived a year after being diagnosed with COPD at the age of 67 and died at the age of 68 due to COPD since the COPD was too severe.