An old dog can indeed learn new tricks. In my forties, I have taken up two activities that would have been much easier and maybe even more beneficial if I had taken them up (or, in the case of the second one, kept up) in my twenties: strength training and guitar playing. They have taught me some valuable lessons.
Both of these activities are physically painful in the beginning. Guitar requires you to press strings firmly to the fingerboard with your fingertips. This hurts your fingertips until they callous over. It also requires your fingerboard hand to perform feats of gymnastics that hurt until you develop the necessary strength and muscle memory to do them easily. This is especially true if God gave you diminutive digits, like He did me.
In the case of both strength training and guitar playing, there are only two ways to get rid of the pain: either quit, or keep practicing until the pain goes away.
But the biggest lesson I have learned is about the nature of progress. After I started strength training a couple of years ago, I reached a point where I felt like I just wasn't getting anywhere. Nevertheless, I persisted. Then, one fine day, I suddenly felt different. I felt like my muscles, rather than my excess fat, were in charge of my movements. So I kept on keeping on. I have continued to run into periods where I feel like I'm falling apart, but I can't quit, even when the rewards seem minimal or non-existent, because I now know from experience that I'm a lot better off with the training than without it.
It's the same with the guitar. I am still far from where I want to be, and I still have some overall struggles. I run through a piece over and over and still hit potholes, always in the same part of the road. Sometimes I feel like I can't get my fingers to obey me on anything. But the lesson I learned through strength training holds here, too. The problem areas are still problem areas, but they gradually get easier if I keep practicing. As long as I persevere, one of these days, they won't be problems anymore.
Progress, then, may be completely imperceptible. It is the watched pot that never seems to boil. Making progress is like crossing a wide, featureless desert, where the land looks the same from horizon to horizon and you can't tell how far you've come, until suddenly you reach the water's edge. Sometimes progress even takes on the appearance of regression, because there are difficulties that can only be encountered and overcome once you've reached a higher level.
Infused expertise is a rare phenomenon, so if you take on strength training, or guitar playing, or the project of mastering any skill, you will make a great many mistakes. But unless you clearly have zero ability whatsoever in your chosen area, the biggest mistake of all would be to just give up.