Can you clarify the carseat laws for children 0-4yrs for me please??

I have been discussing what the laws are regarding turning baby car seats. We can't properly clarify what the actual law is. Is it when babies reach 8kg, 9kg?? Any child over 6mths?
My DS2 is 9mths old and 8.6 (ish)kg. We have recently turned his carseat. I have been reading different sites as to whether it's legal or not and I can't make sense of it. I think it is because he's over 6mths, but weight wise, I want to make sure it's advisable by law. I know it's advisable to keep them rearward for as long as possible, but for me it's not worth the argument from DH (yes he's seen the vidoes and stuff about it all and is still not swayed to keep him rearward :(). But if it's not 'legal' by weight limit, then I don't need to argue, just say it's illegal!

I think unfortunately legally its purely age - 6 months and they can be turned forward-facing. Can you tell your DH a bit of a white lie and tell him its not until your DS reaches 12kgs?

the law is that they have to be 6 months of age and at least 8 Kgs to turn around :(