Why does emphysema continue to worsen even after i stop smoking ?

Yes: Yes but at a slower rate (approx 1 tablespoon of lost lung function per year).

Lung Function: Everyone's lung function declines with time. Everyone: with or without lung disease. The problem is, those with emphysema can lose their lung function at a faster rate. And that happens even if you stop smoking. Thats the unfortunate thing with smoking.

It doesn't : First, if you're 25 and have emphysema you should see an expert because the diagnosis should be questioned. Second if you do have emphysema and you stop smoking it will not worsen.