I won a small claims case in San Diego almost 20 years ago, lost track of the defendant and hbe now reconnected. I never received payment from him. Am I past the time limit to
Collect?

A California Judgment is valid for 10 years and renewable for 10 after that.

Did you renew it? If you did not it's out of date.

Since you make no mention of renewing it, yes it is too late to use any legal enforcement though the courts, That does not mean they don't owe it, you just no longer an do things like garnishment or attachments.

You may send them all the bills demanding payment you wish