If you are lending your own money, you do not need a license. However, if you are arranging deals for others, you do need a real estate broker license for the operation.
I am a licensed Calif. DRE broker and would be glad to discuss the requirements of such an operation with you in detail. Private money lending brokerage is very interesting but can get pretty involved and I have had hands-on experience in this field. It all depends on how involved you would like to be and what your goals are.
It is also important to know the origin of your interest in this type of business. As you probably know, there are many private lending operations in California. Some thrive, and some go out of business. It all depends on how right things are handled. Anyway, I will glad to hear from you to share futher details.