Wouldn't say 6th grade comprehension, You would need atleast an 8th-10th grade comprehension level and you can definitely understand most of the internet and it'll help you talk English with precise wording and understand academics and theories in subjects which use complex wording easily which a 11-12 year old couldn't.
This tbh, I haven't learned any English for like 10 years probably, I started to watch English YT content a few years ago and it def helped me a lot, watching movies or anime or whatever and looking up stuff you don't know might be a great help, and as @The Wife mentioned I can recommend Babble personally too, if you want to save money just buy it with a Brazil VPN cuz they have the cheapest price there AFAIK