Question

we have not used the medicine for ages.(change to passive)​

Answer 1

The voice of given sentence can be changed as shown below:

The medicine has not been used for ages by us.

Explanation

The verb in the sentence was in Present Perfect active voice form (have you finished). When we convert the active voice of Present Perfect into passive, we use passive form equivalent to the active form. The passive form in Present Perfect is has/have been+V3. The object is made the subject and vice versa; and 'by' is added.

Present perfect active = has/have + V3  

Present perfect passive = has/have + been + V3