Some people don't know about bitcoin while others know the name but don't know the reality whereas most of the people know very well about Bitcoin but due to volatility they ignore its benefits. It does not mean that those who don't have invested in Bitcoin don't know about it but some people don't have money to invest in Bitcoin so they cannot utilise their knowledge to get profit from investment in Bitcoin.
I think the old people don't believe in Bitcoin easily because the thing which is not visible with the naked eye is not trusted for them. Bitcoin is one of the best investment tools and there are no boundaries for anyone but still people are afraid to invest in it.