I haven't smoked for two years.

[lagoo]

(1) I don't smoke now and my last smoke was at least two years ago
(2) I do smoke now but I didn't start as long as two years ago

The explanation is hard to understand. Why is it ambiguous?

 

[emsr2d2]

Neither one is clear. I assume that they mean:

1) I don't smoke anymore. I gave up at least two years ago.
2) I smoke. I started [smoking] less than two years ago.

 

[Tdol]

I only started xxx time ago would be a better way of showing how little time you've been smoking.