The average life expectancy for Americans is 79. In the US at least we define "senior citizen" as over 60 (legally and for healthcare), that seems like a reasonable age for elder to start.
As to your question, yes. Even if it was 90% of the population that was 60+. being an elder, senior citizen, a member of the grandparent generation, olds, or whatever you'd like to call them has more to do with the individual's age than how many of them there are.