This post reminds me of the Oscar Wilde quote, "I am not young enough to know everything."
In reality, there are plenty of excellent older developers around who are still building stuff. They just aren't building it at the kind of company where you reach the most senior recognised development position after as little as five years, you've run out of interesting problems to solve in half that time anyway, the management think productive developers are the ones who work so many hours that they can't have a family and/or social life at the same time, and the junior developers think grandpa can't program with anything invented since COBOL.
Meanwhile, look at the guru everyone turns to in a small-to-medium sized shop, the top-billing freelance/contractor/consultant crowd, the disproportionately successful founder demographics, and the guys who are lecturing everyone else with "Fellow" in their title at the bigger technical firms, and you'll find plenty of places where the very experienced and capable hackers are still plying their trade quite happily.