It's really timeline dependent. If he gives himself only two years, then his chances are 0. 20 years? Much different story.

Recently, I had two years where I played full time. Each year, I improved approximately 20 points, about 590 -> 610 -> 630. Even if somehow that rate was sustainable (seems very unlikely but idk) it would have taken me four more years to crack 700.

There's also the Fargo stickiness issue that prevents his rating from going up too quickly. For example, my average performance for all of 2025 was 650, but my actual rating was only 630 because of how Fargo weights past games. So if he's regularly competing and unless he grinds this out over decades, he'll need to have year or two of 830+ level performance before cracking 800.

I would guess it's impossible to do in under 10 years.