My dad went from being an auto mechanic to learning to code when he was 63 and he's 77 now and argues with me about Drupal vs Joomla over dinner. It's only one sample but I'm convinced him switching careers extended his neural plasticity considerably.
I'm not saying you do, but I have found the general public vastly underestimates the intelligence of many auto mechanics--especially today's mechanics. I guess they have always been an easy target in movies, etc.? I have a feeling your dad could learn anything if given the right structure. Mechanics are underpaid, expected to continually learn on their time, provide $20,000-30,000 grand worth of tools; and the owner…
It was fun, too; much like debugging code with your hands. Okay, what evidence do I have to work with? Of these several hypothesises, which are the most likely? And, just like code, sometimes you spend the afternoon going down what you thought was the right path only to find out you're wrong.
As with software, there are hot shots that just seem wired for the task, and there are those that can merely competently do the job without screwing it up (and, like software, there are those few you don't want anywhere near your stuff). Just like software, I was one of those that fell in the middle. :-)
Tell ya what though, unlike software, I had very few bad days as an auto mechanic. Decent money, I enjoyed the work, and when the weather was nice we open the bay doors and you're practically working outside. Rarely did anyone second-guess my decisions (and when they did, it was to make my job easier so I don't do it the hard way), and I rarely had to convince anyone of my estimates as we had a big book that already estimated how long a competent mechanic should take to do the job.
One big difference is that incompetence is harder to hide as an auto mechanic. You're not going to be doing any copy-pasta from StackOverflow when you're an auto mechanic.
Smart? Eh, like anything, it's hit or miss. Since the repair bays are right next to each other, and you don't have to expend a lot of cycles thinking through hash table algorithms, there's plenty of talking. Mechanics are a reflection of the general population, some guys (and they were all guys back then; girls worked up front behind the desk) I knew could probably write philosophy books, others probably won't be moving to Microsoft to write kernel code any time soon.
In summary, the public underestimates the intelligence of just about everyone but themselves, so mechanics don't get a pass. Nor do the mechanics care about what you think, at least this one didn't. I was happy where I was at at the time, I didn't need anyone's approval. And the money was good.