Legal Question in Criminal Law in California

Re: selling drugs in the past

Not on that basis alone. To get a conviction, prosecutors would have to prove beyond a reasonable doubt that he made a particular sale, not just that he used to sell marijuana during some part of his life. They also would need admissible evidence of the particular sale; the unsworn statements of the defendant and others on various websites would not do it.

If the police and/or D.A. are particularly interested in this person -- perhaps because they think he is guilty of other crimes they can't prove and they want to at least get him for something, or because they hope to pressure him into becoming an informant against someone else -- they might use the information you describe as the starting point of an investigation. Otherwise, this seems like a lot of work to go through for a small time dealer who stopped dealing a year ago. Anything is possible, but I don;t think a prosecution is likely based upon the few facts you have provided.