I see no advantage graduating early and many disadvantages. As stated by the above posters, you will not have a complete UC GPA since they use only 10-11th grades in their GPA calculation, you will have less HS course rigor which is Very Important in the application review and meeting the a-g course requirements is not enough. You are required to take 15 a-g course requirements (30 semesters) but if you look at the Freshman profiles for all the UC’s and especially UCLA, the majority of applicants have 50+ semesters of a-g courses on their application which is additional 10 courses beyond the minimum.
If you have exhausted all your HS course offerings, then consider Dual Enrollment at your local CC. Also having an extra year for EC’s will only strengthen your application.
Best of luck.