What keeps me going? There is just so much interesting stuff going on with computers - how can you ever get bored :)
There are a lot of people better than me, also younger than me, but I can still knock out solid code. I think not thinking I have mastered something keeps me going. There is massive churn in languages and technologies, all my COBOL / FCS / IBM Mainframes skills are consigned to the dumpster but they help me learn new things like C / CP/M / MSDOS / Assembler. Which got dumped for Unix (not Linux) / Macintosh (pre OSX) / Prolog / Lisp / C++
I'm now doing Python and Ruby on Rails and learning Nim and Virtual Reality
What a time to be alive!
Age discrimination - can't say I've noticed it but I've always expected to be judged by my abilities not may age. Perhaps I've been lucky