Code is the author's though processes made concrete (in a sense), and some people just think differently, some people are just incompatible. Over the years I've seen some codebases considered good that are easy to follow and I like them, and other codebases considered good that just seem to grind my mental gears even though I can't put my finger on any specific problems with the code.
I'm also turning 40 this year! You may want to look up crystallized intelligence (wisdom) vs. fluid intelligence ("raw" power) (https://psychcentral.com/lib/what-is-emotional-intelligence-...) and let those concepts process for a bit. We tend to move towards crystallized intelligence as we age, which has many advantages that folks are alluding to here. The key could be to recognize the difference and where your current strengths lie without wishing for the past (probably fictionalized) you. You are who you are now, not what you were. Be mindful and appreciate the experience and strengths you have now that you didn't as a younger person. You might try to organize your work, and maybe eventually change your job/position/title, so that your current strengths are aligned with the expectations. In other words, you don't have to keep trying to be a great programmer, but you might become a great mentor, manager, author, oyster diver, etc. It's the reason many move from engineer to manager or musician to producer. You can actually be much more effective and valuable if your experience can help inform many people's code rather than just your own. You may also want to think about how great it could be not to even try being the "best" programmer. What a relief! Now you can focus on what you care about in your field and perhaps turn your focus outward towards helping other people instead of simply building your own resume.
Code is the author's though processes made concrete (in a sense), and some people just think differently, some people are just incompatible. Over the years I've seen some codebases considered good that are easy to follow and I like them, and other codebases considered good that just seem to grind my mental gears even though I can't put my finger on any specific problems with the code.