At what level of running experience/skill would you start training for a marathon

I (F 16) started running in October and running regularly in January(30-45 weekly). I really want to run a marathon but I am not sure if it’s save/ reasonable to start training now. My longest run was 21.1 km, which I have done 3 times now. My fastest time was 2:09 but it was not an all out effort.