What does that tell you? It tells me that if you've learned certain things, you can't learn anything new.
How foolish is that - both to believe about others or worse yet, to believe about yourself.
You can always learn new things. I was so proud of my mom when she was 80 years old and wanted to learn how to use the computer to email and write letters and even play games. She surely was what is considered an "old dog" but she wanted to learn new tricks.
I find this phrase both insulting and limiting to me (I'm old...ha ha). But it's also a sign of laziness. Sometimes you have to take more time to try to teach those new tricks to an old dog.
In my "dog" experience I've found it easier to teach my older dogs than when they are puppies. Maybe that's because they are Siberian huskies though - a stubborn breed to say the least.
Wipe this phrase from your mind. It will serve you to explain why you might not be able to achieve some of your "success list" if you let it seep into your thoughts. It's very much saying you can't learn or teach others to come along the path you're showing.
You CAN learn new things and you CAN influence others to learn new things. Do NOT make excuses anymore.