I've only known a handful of 90+ people in my life. Only one of them drove and he was a rolling hazard for years. (Died at 94 from natural causes. I personally forbade anyone in my family to be his passenger -- ever.) Several of them didn't stop driving until something bad happened.

I've lived in a retirement community via care-giving for my aged mom for almost twenty years. The number of incidents I've personally witnessed in traffic among this group are astonishing in their frequency. Thankfully, due to the care and caution of others, usually nothing happens. I can tell you, in all seriousness and without exaggeration, if not but for my own care and caution, I'd likely kill or injure at least one a day.

I don't know anything about the man you're talking about. Surely everyone's different. Maybe he's fine. However, I agree with your opinion that it would be a little risky. I suspect very likely unreasonably so. Whether or not you're being a "brat" about it, I can't speak to.

Here's another take.

After driving truck 36 years and a couple milyn miles I am quite sensative to potential road problems criminal and otherwise having survived several of both:

Regardless of driving ability an obviously old person is quite vulnerable to being run off the road or otherwise attacked. Age will dull the ability to detect a potential criminal problem. Their age is obvious and reactions certainly are not up to par if it came to evasive action whether traffic road problems or criminal intent.

The main problem is that the reaction time and the reflexes are so much slower that they are usually unable to avoid an accident when something unexpected happens.

On an Interstate with the usual Interstate traffic and speeds, he could cause trouble. It's not a case of being a good driver, it's Old Mother Nature slows reaction time down.

They can't brake fast enough, or turn the steering wheel quick enough. If they drive slow enough to control their car, they will be too slow for others and may get rear ended.

97? NINETY-SEVEN?

And what does "three states away" mean, exactly? 100 miles? 500 miles?

So what if his trip is uneventful except for the accident that he caused, yet wasn't involved in?

In simple terms, I say "No Way". He can hire someone to drive him, but no, he shouldn't be one the road that long for all the reasons mentioned by the other excellent posts.

Can't help wondering: "Across 3 states"
Will he be starting from state '1' or state '0'?
Is the finish in state '3' or state '4'?

My dad is 84 and we won't ride in a car with him.

Things you haven't told us -- his vision, general health, activity level, current driving habits (frequency, distances, accidents, etc.), the distance, the roads and amount of traffic on them, and how many cities (traffic)/rural areas (isolated if needing help) would he be going through, an does he use a cell phone (really use one), have an in car assistance service, GPS, etc.

I would tend to say no, but I could be swayed.

This afternoon I heard a presentation for a volunteer-based senior transportation service, a local branch of ITN, a senior mobility organization.

http://www.itnamerica.org/

In our county, 57% of ALL accidents that involve injuries or fatalities are caused by senior drivers. Does that give you food for thought?

Here is a link that might be useful: Older driver factsheet

I would no more allow a 97 year old on a trip alone than I would expect a seven year old to travel alone. Even if he can safely drive locally, he should never be driving long distances. His eyesight and reflexes are not the same as when he was young, and he could get distracted or lost on unfamiliar roads. My Mom stopped driving when she was about 80. She had a minor accident in a store parking lot and it really scared her. My best friend's Mom drove until her death at 86, but she drove only in her own town and one one adjacent town. She drove only for hairdresser appointments and to do her banking, short local errands.