I dont think i started revising till a month before GCSEs, but dont do that! But you certainly dont need to start in year 9! Make sure you revise for mocks and then have a break for like a couple months and start again and you will be fine! Do your homework you are clearly dedicated and motivated so don't stress.
Half of GCSEs is exam technique. Learn passively all the time like stick the names of objects in french around your house if you are learning french for example. Or stick equations or formula you need to know somewhere you look everyday!
I found the best revision for me was practise! I didn't have a problem with content, just the exam technique so I went on physics and maths tutor and did all the questions there ever was for the subjects I was studying, admittedly I only did this for A Level because I was not bothered and super lazy during GCSEs. For English I did however find like 5 quotes memorised them and then memorised points to make in essay on nearly every question they can ask you. So like Of Mice and Men there is a quote "Curly's wife had a red dress." I could relate it to sexism then and now, she doesn't get a name, she is curly's property, the heirachy then, its a book written when racism was prevalent yet she doesn't get a name. The red is foreboding, or symbolises passion. I could write about foreboding, love, sexism, racism, Curly's relationship with her and Lennie's relationship with her as well.
My best friend was awesome at exam technique not great at the content, she mad tonnes of flashcards and posters etc.
A technique we both found useful was summaries an entire topic onto 1 A4 sheet, write in colours it helps, doesn't need to be need tho. Then do exam questions, anything you wrote on your sheet that didn't come up probably didnt deserve to be there and extra stuff like exam technique was written in red. She would rewrite the sheets to be neater, I was lazy and didnt, but we hung them up on the walls of our bedrooms and then passively learnt the sheets whilst actively learning other topics. We could take the notes to our lessons or right before exams etc.