But, truth be told, unless it's in mini private key format, your odds are allmost 0 when you can only read 9 characters... (and even if it's in mini private key format, it'll probably take more time and effort than it's worth... I didn't do the math, but my gut tells me that even in this case, it's allmost impossible)
Even if it's a mini-private-key, it's impossible to brute-force from 9 characters.
The thing is that it is old-washed paper and I can read only the first 9 symbols of this string.
You'll need to find a way to read the other characters. Try bright light, adjust the contrast on pictures, or get a microscope to look at damaged paper fibers. I made up that last one, I have no idea if that's possible, but it's more likely than brute-forcing the private key.
Is it possible to retrieve his Bitcoin with only that fraction of a private key (the balance is 1.09BTC)? How long would it take to brute force the rest of the private key?
Without doing the math, it's safe to say it will take
forever and cost much more energy than 1.09BTC is worth.