Thank you for your question.
If you plan on having the title
of the car remain in your name, then you do not have to register it in California. However, if you plan on giving him the title to the car, he will have to register the car in California.
Any vehicle owned by a California resident must be registered within 20 days of entry into California unless a special permit was obtained. Nonresidents whose vehicles are properly registered to them in their home state or jurisdiction may operate their vehicles in California until they:
Accept gainful employment in California.
Claim a homeowner's exemption
Rent or lease
a residence in California.
Intend to live or be located here on a permanent basis (for example, acquire a California driver license, acquire other licenses not ordinarily extended to a nonresident, registered to vote).
Enroll in an institution of higher learning as a California resident or enroll their dependents in school (K-12).
Please let me know if you have additional questions or if you need more detail.