Actually, it is exactly the opposite, just because you need to spend almost entire life (at least most of your time) to become a real pro in any field, say a medical doctor or system engineer, or philosopher.
'Start early and evolve' is an universal mantra, which is correct in sports, music, languages, communication skills, etc. So, the idea is very simple - stay near your field and do not try to compete with those, who were spent half of their life on it. Or at least do not try to teach. =)
You wouldn't join the boxing championship just because you're famous computer engineer? Would you? =)