Good to hear some good news. As stated, make sure you take care of the old feller. You know him better than we do, so give/help with what you know he needs. These types of relationships are becoming more and more rare. You obviously know and appreciate what you have. Happy New Year!
And I would be cautious about offering more than he asked. An old-school good guy might be insulted and interpret it as you think he needs charity, and that would damage the relationship. I had a friend from church out here with his kids a few weeks ago. We've been on a lease together and know each other pretty well. He wanted to pay me to hunt next year. I was cool about it, but, I doubt I'll invite him back.)
I agree on this point of view 100%. To further the discussion, if the lessee is paying below a fair market lease rate (even with the 20% increase), wouldn't a "stand up guy" on the other side of the ball try to pay what is fair knowing they are still below market?
There are some intangibles to consider here as well - trustworthiness and what sounds like a great friendship between landowner and hunter has an immense value. Two stand up guys should be able to have a forthright conversation about being fair to each other.
I had 1/4 of the acreage of one of the places I lease sold off to a neighbor. Landowner was under no obligation to let me know, but after a decade of leasing and working cattle with him, and having close family friends in town, I would have figured I'd make the short list of folks to notify. I would consider him a friend, but that move soured my perception of our relationship.