age     X1   X2
age 0   2    2
age 1   2    2
age 2   2    3
  ...

age 0  age 1 age 2
X1    2      2     2
X2    2      2     3
     ...

data <-structure(list(age = c("age 0", "age 1", "age 2", "age 3", "age 4",
"age 5", "age 6", "age 7", "age 8", "age 9", "age 10", "age 11",
"age 12"), X1 = c(2, 2, 2, 4, 7, 12, 19, 22, 18, 11, 6, 3, 3),
    X2 = c(2, 2, 3, 4, 8, 14, 21, 24, 20, 12, 7, 4, 3)), row.names = c("0",
"1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12"
), class = "data.frame")

library(tidyr)
wide <- spread(data, age, X1)
#X2 remains the same, and X1 is not correcty reshaped.
wide <- spread(data, age, X1, X2)
#Error in spread.data.frame(data, age, X1, X2) : object 'X2' not found