That's a tough one, as each individual is so very different from another.  My Dad and I had the same issue.. come winter time when the days get short and the wind gets cold the evenings become way too long.  You look up thinking it has to be 10 at night and it's really just 6:30 or something.. Messes up your internal clock.  I can't imagine feeling like that year round at any age.  Dad retired from the USAF after 20 years (just before I was born) and went back to the farm with my grandfather.  I never knew anything else.  I did 8 years in the Navy and then came back here to farm with him (grandpa died when I was 16).  Dad was moody in the winter months the last few years, though we managed to keep busy with feeding and working on or building new fence on all but the worst winter days, or work on some things in the old shop when it wasn't too cold to keep it comfortable.  He always told my Wife an I, if the time comes that I can't work, at least a little, I don't want to be around.  I don't want you loading me in a truck and parking me at the edge of a field so I can just see what's going on.  Dad left here last week of April last year, after an afternoon of us working on the sprayer to get ready for burndown.  He went home, ate dinner, got in his recliner and had a stroke 2 hrs after he left here, and never came to again before passing on May 4th.  He literally worked until the last day, just the way he wanted it.  We always joked we'd find him in a cab somewhere, up against a tree or off in a ditch, and we weren't far off I guess.  He was two weeks past his 79th birthday when he had the stroke.  79 seemed so old when I was a kid, I'm just 37 and it seems like it's right around the corner, and my Dad, despite major back surgery, and 2 open hearts since 1999, never missed a day of working aside from the days mandated that he couldn't following any of those procedures.  I think I talked him into quitting before me one time, his last planting season, 2014, I finished disking and he was about 20 acres behind me with the planter.. and it was about 8 pm.  I finally conned him into going on home, and I'll never forget, I was 4 acres from being done, just had a little dogleg left to plant, and it was a farm I had just picked up, first time on it.  There was a "finger" sticking out into this field, had three gigantic trees across it, spread 40 or 50 feet between each, and I could drive around where I'd already planted or just cut through the grass.  10:30 at night, and I cut across.. got halfway across and the tractor just sank.  All the way to the drawbar.  I really thought it would take the dozer to get it out, and I sure didn't feel like going home 14 miles to get it loaded up and brought over, and there was a shot at some rain.. so I called.  He was watching a baseball game, and laughed his rear-end off when I told him I'd done.  He came on and we were able to pull it out with the tractor somehow, and I told him to go on home, I'd be done in less than an hour lord willing.  He said "Nah, think i'll stay with you, it's a long drive back when you screw up again!"  He was still laughing.  He never left me again until he left me for good, and I knew better than to even try to send him home.  Sorry for the rant, coming up on a year of him being gone and the story just came to mind.  As someone said above, sometimes all you've ever known to do BECOMES you, not just what you used to do.  When that happens, sometimes the only option to maintain your sanity and identity is to do what you know until you can't do it anymore, and for the lucky ones, they get to do it until the very end.  My grandfather wasn't so lucky, he made it until 78, visiting the farm, gardening and mowing his yard, and then the alzheimers took hold, we had him at our house for about 8 months but then he became very aggressive late in the evening and became too much, and he spent the last two years in a nursing home, and at the point he didn't really know us anymore.  You could tell that he knew we belonged there, but he just couldn't put 2 & 2 together to associate who we were.  What little recognition he did have, wasn't correct, he thought many times that one of his sons was his nephew 40 years earlier.. In the early stages he'd mow in the day but ask in the evenings if we had put the mules in the barn for the night and milked the cow.  He was going back around 60 years during what they call sundown syndrome.  It was really sad to witness.