I honestly doubt that a team of diverse engineers (young and old) would have a hard time figuring out whether it is a graph problem in a reasonable amount of ti

I honestly doubt that a team of diverse engineers (young and old) would have a hard time figuring out whether it is a graph problem in a reasonable amount of time with the internet at their disposal under normal working conditions. The interview isn't set up that way and introduces non-natural pressures that can easily alter the way a good engineer responds to such a question. I would think younger candidates have likely been more recently immersed in problems such as graph problems and tend to be more aware that they need to spend time training on leetcode or hackerrank in order to pass an interview but I don't know. You could always still get lucky or be making decisions for reasons you aren't aware of.