这个作家戒烟多少年了?
当since作为连接词后跟从句,从句中用持续性动词的一般过去式时,主句用持续性动词的现在完成时时,就表示自从从句动作结束时算起,比如：
There has been a lot of changes in the village since I lived in it.
自从我不住在这个村子以来,这个村子里面发生了很大变化.
It is three years since my mother was a teacher.
我母亲不当老师已经有三年了.
希望我能帮助你解疑释惑.