as.numeric() does not convert your object. To convert it, you would have to reassign the output to your object, for instance with:
date <- as.numeric(date) or
date <- date %>% as.numeric() or
library(magrittr)
date %<>% as.numeric()
or with a mutate() or map() function.
After running as.numeric() on it, your date is unchanged (and so in the same class) it was before:
date <- as.Date("2000-01-01", "%Y-%m-%d")
str(date)
#> Date[1:1], format: "2000-01-01"
as.numeric(date)
#> [1] 10957
str(date)
#> Date[1:1], format: "2000-01-01"