Same. When I was 18, I already started to experience deteriorated focus and cognition compared to my 13-year-old self. I remember being able recite the names of commands, software projects and libraries with perfect clarity at 13, with a strong ability to connect the dots (for example, if I read a technical concept in one book, I could probably recognize it when I had encountered it a month later). When I was 18 it became worse.
I first discovered it after realizing I was serious confused by two programs with similar names in the middle of an IRC conversation in a FOSS-related channel. The mistake was so embarrassing according to my own standard, I knew both programs and I couldn't even believe I could confuse them, yet in the conversation I was totally blind to the mistake until someone started to question it. It was when I realized and accepted the inevitable. Interestingly, I don't remember feeling sad - I knew the same IRC channel had members who were younger than myself, yet they were able to discuss technical questions with me at the same level, if I was replaced by them, nothing of value in the FOSS community will be lost.
I first discovered it after realizing I was serious confused by two programs with similar names in the middle of an IRC conversation in a FOSS-related channel. The mistake was so embarrassing according to my own standard, I knew both programs and I couldn't even believe I could confuse them, yet in the conversation I was totally blind to the mistake until someone started to question it. It was when I realized and accepted the inevitable. Interestingly, I don't remember feeling sad - I knew the same IRC channel had members who were younger than myself, yet they were able to discuss technical questions with me at the same level, if I was replaced by them, nothing of value in the FOSS community will be lost.