For me a generation gap is about 13 years. And this is because way back around 91-92 India changed. We liberalised our economy, Cable TV came in, Multinationals(mostly American) set up shop, the seeds of the IT boom were being sown, et al.
All this started changing the way we were thinking. It was as if someone had taken off a blindfold that was over our eyes. Kids of 12 -13 cannot remember a time when there was no cable TV, when the only cars they saw on our roads were the old Ambassadors and Marutis, when telephones had to be 'dialed' not punched, when a girl wearing jeans to school would be given a second look , Computers were not to be approached with shoes on for fear of dust polluting the CPU, when India was so different.
But, I guess that this gap changes across different continents, maybe for the Russians the gap may have begun with the fall of the communists and maybe in countries like Iran or N. Korea there is still no generation gap...
I am not sure if there is some other method of calculating how many years a generation gap is? Any ideas?