Legal Question in Family Law in California

As long as he is above the age of 18 and not a party to the action, he can serve the papers. The term "party to the action" has been construed broadly to include people named as protected people in petitions for restraining orders, so if you are seeking to have a restraining order prohibiting her from contacting him, he cannot serve the papers.

Just to add one more small fact - you may not charge the other party for the expense of service by a non-licenced process server. If you win your case - or the court believes it is equitable to allow you that fee - process serving is considered a recoverable cost that you may be awarded. So do not ask for process service fees as you will not recieve anything (unless he happens to actually be a licenced process server!).