You guys forget that non-citizen/resident engineers only take the FE when they come to the states. This includes experienced licensed engineers from abroad that then decide to start their licensure process in the US (Arup/AECOM/Bechtel and lots of other big guys have people like this). In addition, there is a big group of international graduate students that take the exam after their MS/PhD degrees, they may or may not join the workforce, but it drives the average age up for the FE.
I myself took the FE after my MS (I was 23). PE @ 26, will be 31 in Oct 2020 for the SE.