Three of the ten data points in the following data frame are above 65. The calculation returns 0.3, not the average of the ages.
DF <- data.frame(age = c(13, 67, 23, 45, 78, 35, 21, 80, 64, 2))
mean(DF$age > 65)
#> [1] 0.3
Created on 2020-02-05 by the reprex package (v0.3.0)