Los Angeles has lots of options in comparison to most areas of the country including but not limited to private schools , public gifted and HG/PG magnates, public SAS (schools of advanced study) and homeschooling groups. I don't know of any gifted charters, but there may be. There are also some 2e options for older students.
My DS attends an SAS school where they allow him to do self-guided independant study projects and have assigned a 1:1 math tutor since he is doing middle school math. They allowed him to join upper grades for Friday electives to allow an escape from a more boring unit and study aerodynamics which appeals to his scientific mind. They have also been able to address areas of slow skill development or in some cases to skip over things he finds too boring to focus on and allow his motivation to carry him through a more challenging level to keep his interest. I don't know if there could be a better program for him except that he is still a bit lonely, advancement may help him socially. He likes to work at his level but he is not necessarily looking for a 'rigorous' or high pressure environment.
