They are willing to pay to avoid old.
The underlying reason is that young fresh grads are running circles around old timers.
I hate to say this, but in quite a lot of circumstances, ageism is very well justified for these reasons:
1. IT/CompSci is constantly changing and high growth area, any engineer worth his/her salt will grow rapidly.
2. High performance old-timers have either retired (earning their $$$) or moved up the ladder to manager/director/VP/Founder levels.
3. Regular IC old-timers who have not progressed in their career - companies don't want them, because old-timer who has not grown in his level - is a red flag for companies.
4. There are some old-timers who prefer part-time/consulting type gigs, but I put them in Founder category, all of them have their own LLC/S-corp and run one man consulting/entrepreneurship shop
Everyone knows that old dudes can’t code.
The biggest extracurricular project that I did, was first released in early 2009, and is still picking up traction, this very day...
Depends on what you want. Some stuff should not be designed for the long haul, but some, definitely should.
Just reading some of these comments, makes me happy I have made the choices that I have made.