With car sharing you are more likely to wear out the drive train then the car getting outdated.
It's not "outdated" so much as "the interior is falling apart." Have you driven many higher milage cars, or (in a moment of misguided charity) let people borrow them for extended periods of time?
You run into things like the power windows (luxury!) not working right, or the manual windows sticking because the guide track is worn, the seats being beat up/ripped from use, general stains, the steering box being sloppy, etc. It's not (usually) drivetrain issues - even on really high mileage cars. There's certainly a survivor bias there, and you won't find many high mile Taruses of the "has a weak transmission" era, but the whole car wears out, and putting a million mile drivetrain in a car doesn't magically change that, by 300k miles, it's pretty beat up. Ride "sharing" services will be even worse, because you'll have people who truly don't care about the car, because it's someone else's car. I don't think we really see this with Uber/Lyft right now because the car owner is in there keeping it neat, but if it's self driving? Some percentage of people will be really rough on the car, and that's going to be a problem.
Can you put a price on the safety of your spouse or children? I know I can't.
I can and do. We don't drive a German luxury car, even though, if I were to abandon all long term financial goals, I could "afford" one on a cash flow basis. We drive something less expensive, optimized for our driving needs (currently a 2012 Chevy Volt, because my wife and kids do quite a few 20-30 mile days, which they can do mostly on electric). It's reasonably safe, but it's not the "safest" car on the road, nor does it have a lot of advanced features. They're of fairly limited use out in the rural area we live in, and aren't, to us, worth the money it would cost to get them.
Reliability: it's just reality that as a car ages it becomes less reliable than it was previously. Wear and tear is a real thing. With reliability again comes safety as breaking down on the highway is not the most safe experience to be had.
I've driven some
genuine shitboxes in my years of driving. In order from least expensive, I've purchased cars for $100, $150, $200, and $350. Then, you know, a genuinely luxurious $2000 car!
In many, many years of doing that, I've been stuck on the side of the highway twice. Only one needed a tow - I was able to fix the other one (a freak failure of a nearly-new distributor cap) because I kept the old parts around. It's simply not that common, and I assume your definition of an "older car" is still quite a bit newer than either "I saved it from the scrapyard" or "I literally bought it from the junkyard."
Service: that's a bit more nebulous but they come to my office and pick up my car, service and wash it, then park it in my spot and give the keys to my secretary; similar for my wife's vehicle. All of this is done with no additional charge. If either of our vehicles needed to be in the shop more than the day a complimentary service loaner, of a new and comparable vehicle, is given to us with no charge. The SA we've had for the last 12 years or so delivers our new vehicles to the house if we want. He knows I know how to work leases and our deals are very transparent, and these days, done via text. No stress and I know the exact residual, MF, and cap cost going in.
Hey, I've got on-site service of all my vehicles too! I service them myself, on our property! :p Saves me an awful lot of hassle, and I bought a house instead of a car that comes with complementary service (a fully loaded Tesla is slightly less than we paid for our whole house).
If you've been suckered into believing that a fully loaded luxury car is a requirement for... whatever reasons, sure. Leasing them is a decent way to efficiently spend obscene amounts of money on a car. But you're still spending obscene amounts of money on a car that, fundamentally, accomplishes the same things my $100 beaters did: Get me around.
I know vehicles with the latest safety features, unsurprisingly, are the safest vehicles.
How much of that is correlated to the age of drivers? In general, "the latest safety features" tend to show up on luxury cars, which tend to be driven by people who can afford them. That generally means older owners (40s-60s), with decades of driving experience to rely on. They're generally safer drivers, regardless of the features in the car.