It could be mental burnout. But you could also get your blood levels checked!
Once in my mid-30's, I found that my mind wasn't as able as it used to be. I could write code fine, but as you, I struggled with learning new things.
It turned out that the hemoglobin level in my blood was low, so my head wasn't getting enough oxygen. The cause was colon cancer. The tumour had been bleeding into my colon for months.
Other causes for losing blood could be ulcer (caused by certain bacteria, stress, too much coffee, fatty food, other stomach irritants), or gluten intolerance (unlikely, but does happen).
Once in my mid-30's, I found that my mind wasn't as able as it used to be. I could write code fine, but as you, I struggled with learning new things.
It turned out that the hemoglobin level in my blood was low, so my head wasn't getting enough oxygen. The cause was colon cancer. The tumour had been bleeding into my colon for months. Other causes for losing blood could be ulcer (caused by certain bacteria, stress, too much coffee, fatty food, other stomach irritants), or gluten intolerance (unlikely, but does happen).