i think if you're a 50+ year old tenured professor, your skills are probably not in line with what a start-up needs; you've spent 25+ years of your life optimizing for doing academic research and teaching, not sweating out the details of making product X work seamlessly on platform Y with quirk Z.

some 50+ year old tenured professors co-found companies and serve in advisory roles, but i highly doubt that they're staying up late setting watchpoints in gdb and punching their monitors.