Obviously if she couldn't comprehend that she hit something that big, that hard there is a problem and she shouldn't have been driving but don't jump to criminal conclusions too quickly. It is possible the woman did not know or was unable to cognitively process that she had hit anything. Medication side effects, Alzheimers or other forms of dementia, stroke/TIA, hypoglycemia, or mental illness/dual diagnosis issues can all wipe out a person's judgement or ability to process information.
It is a misconception that age related changes are gradual, progressive, universal, and predictable but that is the furthest thing from the truth.
First off, chronological age (the number of years a person has lived) is not a good indicator of physical age (the state of physical and mental ability). There are some individiuals in their 80s and a few in their 90s who are more physically and mentally capable of driving safely than some people in their 50s and 60s. Read about the 100-year-old cyclist who finished a metric century with a respectable time for a person half his age
http://www.boston.com/news/world/eur...8RN/story.html
Secondly, changes can be slow and subtle, can come on rapidly without warning, or can be intermittent. Ask the spouse or children of someone with early stage of Alzheimers. Sundowners are people with early Alzheimers or other dementia who are cognitively intact and seem perfectly "normal" the majority of the time but as they become tired toward the end of the day, sundown, their mental abilities deteriorate much more severely than the average sleepy person. After a night's sleep and a good breakfast, they are their old selves again, at least for another 12 hours or so. My own mother went through this and it was very difficult to get her to stop driving. My sister and I knew she wasn't safe behind the wheel but she refused to give up the keys and her condition was quite intermittent. Even if there had been re-testing for seniors, she was probably able of passing the test 75% of the time but she would have "bad days" when she was confused and had lots of problems with memory and processing information. The same problems that clouded her judgement behind the wheel also clouded her ability to realize she should not be behind the wheel. Her condition has progressed and on her birthday just this year she finally failed when renewing her drivers license. Even though she is in an assisted living facility and in no way mentally or physically capable of driving, I have no doubt she would try if given the chance. She honestly lacks the ability to assess her own level of function and believes that she can drive as well as she could when she was 30.
Recently I took mom to the drivers license office to get a new state ID card with her current address because she wants to vote. While waiting, there was a 93-year-old man in line in front of us (I know his age because he announced it loudly several times). He wanted to renew his drivers license but was unable to pass the vision test (I don't know if he couldn't see or couldn't understand the instructions) or even fill out the forms. The DMV employee explained to him that his license was expired but they couldn't issue him a new one so he could not legally drive. He launched into a tyrade about how he had been driving since Henry Ford was still alive and how "stupid" the employee was and how ridiculously complicated they made everything and how no *&%#$@ computer was going to tell him he couldn't drive. He pushed his way through the crowd behind him still rambling, crossed the parking lot, got into his car and drove away clipping the curb as he left.
Medical conditions can affect people of any age and can temporarily or permanently affect cognitive functions. I've seen a hypoglycemic person (low blood sugar) clip a car in a parking lot and then get hung up on the median. After treatment they had no recollection of the incident. There are types of seizures that can be completely missed as they don't cause the grand mal muscle activity but result in brief altered consciousness that looks more like daydreaming or an "Alzheimers moment". The person experiencing such a seizure may exhibit unusual behavior or just drift off for a bit only to startle back to alertness with no memory for the last few moments or even minutes, kind of like when a computer has a glitch and you have to give it a minute to catch up. Once quite a few years ago, I wasn't feeling well at work and clocked out to go home early. I vaguely recall telling my co-workers and boss I was leaving and getting in my pickup but I don't remember the drive home and woke up on my livingroom floor with my jacket still on and a dried up bloody nose. I had a high fever and lost about an hour from memory including the 8 mile drive. Scared the crap out of me but there was no damage to my vehicle and no reports of a hit and run.