(1)He has been a criminal ever since a certain time.

(2)He used to be a criminal.

Either is possible. Present perfect is used for both: recent past ( I have been to two classes today) and continuing existence ( I have been in class since 9 am)
In my interpretation of He has been a criminal, in the sense of used to be, the point is not that the past is recent, but unspecified. If I say He has spent time in prison, I mean that this is part of his past life, maybe even 25 years ago.
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(1)He has been a criminal ever since a certain time.

I know that ever and never are used with the present perfect this way :

Q:Have you ever been to London ?

A:I have never been to london before .

I mean ever is used with the question , and never is used with the answer .

Am i right or not ? please correct if there was a mistake .

Thanks in advance
Yes, ever with the question, never with the answer. This is because ever, here, means even once in your life, while the answer never means not even once in my life.
According to your reply J Lewis , The first sentence isn't correct
(1)He has been a criminal ever since a certain time.
So why Mister Micawber said this "Either is possible"

I wish you make it crystal clear , please .
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A good point. In older English, ever was the opposite of never and therefore meant always. It retains this meaning in expressions like for ever and ever since. For ever = for all time, ever since = always since that moment.
However, in modern English the usual meaning is as I explained. It remains the opposite of never if we consider never to mean not even once, so that ever means even if only once.
Present Perfect is used to show the Present state.

If you say 'ever since' you show how long the state exists, but the state is Present.

If you speak about some events in the Past, Present Perfect shows how the former events influence the Present state.

If the Present state has not been influenced, Perfect should not be used. At least in the given examples.

Take care,