The older I get, the better I understand the saying "you can't teach an old dog new tricks." I used to think this referred to some weakness of the mind or obstinance, which I rejected as foolish and even cruel.
I've come to understand That saying differently. The older you get, the less patience, time, and energy you have with new things. You've seen decades of new things and are beginning to tire of their novelty. You only have so much time, and most of it is taken up with the rest of your life. And you have less energy to spend on something new.
In addition, the older you get, the more experience you have. Starting to learn a new operating system at 20 seems like just a matter of picking up some new tricks, but at 50 you realize just how long its going to take and how annoying its going to be after the previous 5 times through that process. And sometimes it feels like this old Far Side cartoon, where you've filled your mind up with 50+ years of stuff like old phone numbers, how to call information on a rotary phone, and the name of that character on Adam-12.
So its not so much you cannot teach an old dog new tricks. Its that the old dog has been through this once too often and has better things to do.