You must be 18 years of age, you must have minimun of four years witnessed, documented, verifiable experience in the trade your getting your liscense in. You must know California contractual law as well as your craft because thats what will be on your test that you have to pass from the state contracters liscense board. 1/2 the test is craft the other 1/2 is contractual law. Some of the test is on accounting principals. If I remember correct you are given 2 hours for each section of test for a total of 4 hours. After passing the test you will need to get a bond before the state will issue you a liscense. Your liscense as well as your bond are due every two years. You should also get general liability insurance for your company. Of course theres getting a tax id, state board of equalization, and a DBA to register with the state or county(s) your operating within. You will also be required to show proof of "X" amount of $$$ in operating capitol or equilivant in equipment to the liscense board before they will issue a liscense.
The "X" amount of dollars was $8000.00 I believe when I got my liscense years ago. Probably more now but I dont know what that amount is nowdays.
It would be a good idea to pay for one of those contractors schools to at least learn California contarctual law and practice taking the test before you actually take the state test.