Legal Question in Criminal Law in California

Yes, they can allege it. There is no wash-out period. It can be stricken by the judge at sentencing however.

You need a good criminal defense attorney. I'd strongly suggest you find someone who focuses on criminal law and who routinely practices in the court where this case will be heard.

They can try. And you can ask the judge to strike it. (Note that "striking" the prior wouldn't erase it from your record. It would just mean the prior wouldn't count against you when and if you're sentenced in this case.)

The age of the conviction is one factor the judge will consider, but there are others. Your lawyer will be able to advise you about your chances in light of your background and of the charges you're now facing.

Good luck.