I am over 50. But disagree with this notion. Modern coding is surfing over dozens of languages and frameworks. No human knows them all at any age. For me there was a transition needed, where I started viewing the entire internet as part of my brain, and I would not try to know things, but to know where to go to get things. If a programmer does not have this mindset today, they are at an extreme disadvatage. So SO is an ok proxy for active cutting edge programming.