I would rather nervous or reluctant would be drivers weren't browbeaten onto the road by well meaning, but ultimately misguided friends and relatives. If they feel they have poor co-ordination, spatial awareness and struggle with decision making strong arming them behind the wheel of a ton and a half of killing machine isn't really on either for them or other road users.
But a lot of non-drivers have never driven at all, and probably even more non-drivers begin learning but give up because of a bad experience -- an unpleasant teacher, an impatient relative, several failed tests. Driving requires a combination of quick decisions and physical precision, most of which become instinctive over time, but can be very overwhelming at first: I've had a licence for 16 years, but I can still remember how pulling onto a busy roundabout seemed like the most ludicrously complicated and impossible action ever.
It's easy to psyche yourself out, and the less confident you get, the worse you perform, and once you start failing tests it's easy to become very negative and just give up. The worst is often when you get to 2+ tests, because then you put so much pressure on youself I must must pass this time, I've spent so much money and time on this that you're more likely to fail than ever.
But being nervous or reluctant DOES NOT mean you can't be a good, safe driver -- my sister failed several tests in her twenties, stopped trying for so long her theory test expired, then passed in her early thirties and has been a safe, confident driver ever since. And there are so many posts on this thread from people who were nervous or reluctant to begin driving, but who were prompted into learning (by a new job, a new area, kids) and who've also become safe, competent drivers and feel very strongly that their licence is an asset.
I think it's very unfair to imply that nervous, reluctant drivers are just not meant for driving, and they should do everyone a favour and not bother. The idea that you're a menace unless you jump merrily into a car the moment you turn 17 and pass your test after ten lessons is what dissuades less confident people from even starting lessons.
It's really sad to hear about so many elderly female relatives who were dependent on their spouses to drive, and then increasingly stuck and isolated when they were widowed -- this is exactly what happened to my grandmother, but I had no idea it was so widespread. And, no: not a great idea to jump from several decades' non-driving into a car, but if you already have a licence you can take refresher lessons, buy a car which suits your needs, have relatives accompany you at first. You've got the licence, so you're one (large) step ahead, and know that you're capable of driving, whereas a common sentiment amongst older people who've never driven is that 'it's too late for me to learn, now'.