OK, what a great idea you have. And, if your budget can stand it, you are truly looking at a gift that he'll grin about each time his fanny hits the seat.
If it were me, and my dad had the needs you've outlined, I'd do the following. Note that it is the proper attachments, NOT THE TRACTOR (assuming reasonable reliability and proper horsepower), that make all the difference in how much personal effort has to go into getting work done.
Determine if he is very set in his ways about brand of tractor. Some people are. If he is, then that decision is made for you. Or, possibly the options can be cut down since he may have a poor opinion of one brand or another....
For your purpose, unless you find a special situation gently used tractor with exactly the features you are looking for and in SUPERB condition, I believe you are looking at a new tractor.
I believe the following is the general direction... each item is selected for your prime objective... let him enjoy the tractor rather than have to struggle with it.
Get a cab with air conditioning (hay dust can be terrible, also heat/cold)
Get a front end loader with quick attach (ease of use)
Get a bucket for moving materials, gravel, etc for the FEL. This has a very large number of uses. Put chain hooks on the bucket.
If he doesn't have a bale spear for a quick attach front end loader, get one, assuming he does round bales.
Consider a rear 3 point hitch hay fork as well. This way, he could carry two bales at once.
Get extra lights on both front and back.. make sure they are placed so that there is visibility all around tractor, front and rear, even when front end loader and rear equipment is attached. This is a SAFETY factor at his age.
Get three pairs of rear hydraulic fittings. This is a convience feature that gets toward mandatory for the equipment you are discussing. Many TBNérs have increased the number of hydraulic fittings they have afte they have purchased a tractor.
Inventory his existing three point equipment, if he has some and the intent is to keep it, then consider, seriously, a hydrraulic top link. This facilitates mightly the attachment of a piece of three point equipment. My hydraulic top link is a major source of satisfaction for me... and takes changeing implements from a major task with crow bars and sledge hammers to a no sweat (literally) process.
I think you'll be in the 100 hp range.... I know they cost a lot, but having the extra horsepower when you need it means NOT fighting the tractor and equipment when the going gets tough... and that's worth it at his age.
Make sure he has a mobile phone.. a safety item to carry with him while on the tractor.
Make sure that there is a large capacity tool box so that the necessary tools can be close at hand. If tractor does not come with one, you MUST make sure that somehow one is added to the tractor. It's no fun having to struggle to find tools out in the field,
Four wheel drive is, my opinion, a must.
The least leg lifting and moving to change gears and directions , the better. This means a wet clutch/power shift type of transmission is THE way to go, particularly for an older person. This is my opinion and I believe he would learn to use it quickly, even if he is currently biased against it.
Proper tractor weighting is a must... discuss with your dealer and get extra weight added either to the wheels (liquid in tires or wheel weights) at the outset.
Ag tires, of course, are needed.
I love a steering wheel knob on my steering wheel.... $10 item with lots of satisfaction.
You should pay attention to height of step(s) to get into tractor... as flexibility declines with age, this becomes extremely important.
Check the various tractor seats.... make sure that there are numerous adjustmenbts so that it can be positioned comfortably, steering wheel adjustments as well. This is a large impact on fatigue after several hours in the seat.
Give some preference in your thoughts to a dealer that both you and your dad like and is reasonably close by. Many at TBN who have significant mechanical skills, etc. obtain their best price from dealers at a distance from their tractor home. Others swear by using a near-by dealer assuming the price is realistic. I think your situation calls for a closer dealer focused on personal service, rather than a long distance one where service, if needed, would be more difficult..
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By the way, WELCOME TO TBN!!!!! If you have the time, you might expand your personal information so we can determine what part of the country you are in, type of land (sand, clay, etc.) and other information that plays into tractoring recommendations.
There are many great tractors out there to choose from. I'd narrow down to 2 brands based on personal preference or compatibility with the dealer. Then price ALL the features you need and make a decision.
For your awareness, my personal preference is to Kubota tractors for balance of price, reliability, features, dealership service. But, that's just me.
. The other chores mentioned can usually be done as well with 2wd.