There are four stages: mild, moderate, sever and very severe. They generally go by your FEV1 and how often you get sick for the staging. The staging thing is really more to give docs who aren't very familiar with COPD (most primary care docs know less than you do about COPD) a good idea of what should be part of a treatment plan for people who are at various stages.

As Tim's pulmo said, the stage isn't really very important to you. What's important to you is how you feel and what you can do. If you're just now going on O2, my suggestion would be to use it to help you develop a good exercise plan with your doc's help and support and get in better shape. You may find you won't need nearly as much O2 and will b able to do a lot more with a lot less effort if you do.

I'm 73 and I work out every day. Technically I'm very severe, but I travel all over the US and Canada (I fly at least twice a month), I still work part-time as a consultant, I'm a patient advocate for people with COPD and do a lot of conferences and workshops.

you sound so much like me. I too was stage 4 emphysema and on oxygen 24/7, had a portable concentrator for travel and a large one for home use. The VA paid for everything. My quality of life was nil and really didn't have much of a future. I got on the transplant list and received a double lung transplant 7 months ago. A life changing event. Two days post op they took me off of oxygen and I've been breathing great ever since. I realize not everyone comes through it as well as I did, and anything is still possible, but so far, I've been blessed. As I said, the big thing for me was quality of life. Now I can take my wife out to dinner again, or go out with friends and actually hold an extended conversation. I'm not much good but I can even sing in the shower again. If you're ill enough and need some hope, ask your doctor about getting on the list. If he wont refer you, find one who will. Its at least a light at the end of the tunnel. I can give you what you are lacking right now, hope........Just a thought. Sorry if I over stepped my boundaries.

I had emphysema for 6 years, the last 2 were stage 4. I was on oxygen 24/7 and didn't have much of a future. 6 months ago, on July 24, I had a double lung transplant. A life changing event. I feel great and can breath again. I attend meetings with a support group, some members of which received their lungs 10 years ago. All I know is I'm doing great. I'm not saying its a pleasant thing to go through, but would I do it again? ABSOLUTLY

There are only 4 stages. But, 4th stage doesn't mean you don't have any time left. I was told I was in 4th stage 7 years ago. In 2012 I asked my doctor for a prognosis(after being intubated for 3 days), he said that he couldn't give me a prognosis. He explained that no one could because COPD behaves differently in every patient. I did get my affairs in order just in case, but that's probably a good idea regardless of what stage you're in.
Anyway, I'm definitely proof that 4th stage doesn't necessarily mean much.
One of my current doctors said that quitting smoking (I'm successful with that sporadically) and using oxygen as prescribed were key in hanging around for awhile. (I've been oxygen 24/7 for 12 years.)

My pulmonary doctor tells me the same....they are only numbers,on a paper. Use your judgement on how you are feeling, not the numbers.
Exercise is essential.