The SOL in California is 4 years, this is probably past the statute of limitations already.
If this is indeed past the SOL, you can sue him for a FDCPA violation.
If this is not past the SOL yet, you can still sue him for a FDCPA violation if he does not follow through and sue you within a reasonable amount of time.
A FDCPA violation is worth $1000 in damages.

