Today bitcoin is already known worldwide. So we dont need 6 years to be able that all people will be using bitcoin. Were living with advance technology today, and were still uprading every year. It means that even next year bitcoin will be use by almost everyone.
Not amongst ordinary people but only amongst people who are advanced enough on technologies ( even doesn't guarantee all these kind of people know bitcoin ). and next within next year bitcoin will more likely to not used by everyone but becoming minor option and having pretty decent amount of users