Note: JSON is just like XML in that it's a horrible data interchange format ;) And if "knowing JSON" is a key skill you interview for... You possibly might want

Note: JSON is just like XML in that it's a horrible data interchange format ;) And if "knowing JSON" is a key skill you interview for... You possibly might want to ask different questions. Unless you repeatedly build the same thing - see below. Any decent developer, no matter their age, should be able to figure out what JSON is in about as much time as it takes to have a coffee. If they can't do that, you have a real problem. > as a hiring manager why take the risk when someone already has the knowledge? As a hiring manager: Because we're not redoing already solved things, we solve new problems. The person with the knowledge holds the advantage for a few months. And then the person with the problem solving skills catches up. Of course, if you keep building the same type of app over and over - which is fine, and equally necessary - those months are never made up for, and experience matters more than problem solving. Ultimately, you hire for the jobs you need to fill. For my part, I'm happy to take anybody who understands CS and is able to learn over somebody who already knows my tech but is stumped by new problems. (No matter the age) YMMV.