From news articles and personal experience. There have been dozens, if not hundreds of articles about age discrimination in high tech. The people in my extended family who are doctors are all still practicing in their 60s, whereas the two who were programmers were laid off at age 48 and 52, never to work as programmers again. I worked in Silicon Valley, Boston and NYC for 12 years and I can count the number of programmers I worked with over the age of 45 on one hand! (Maybe even on 1 finger, technically the other guy was no longer working as a programmer...)