I was a pretty rubbish reader until 3rd or 4th grade when Legend of the Seven Stars came out for SNES and my sister eventually got tired of reading the dialogue for me. So that would put me in the 10 year old range.
Sibling of someone like you here -- I absolutely got fed up with reading Animal Crossing dialogue for my sister, and I maintain that's the only reason she finally learned to read.
Motivation is one thing -- necessity is another. If you need it (not just want; literally need it for some reason), you'll have a pretty strong motivation to acquire it. (Or give up. But that's where parental guidance comes in.)
My kids reading has really accelerated from playing Roblox. I mean they did read before but they’ve really taken off since. They use Siri to dictate and I surmise they read what she prints. It’s amazing.
