Well, keep in mind that the domain of a function is the entire set of possible values of the independent variable. To make it more clear, the domain is the set of all possible x-values, which will make the function work, and with real y-values as the output. So, the range would be the set of all of the second elements of an ordered pair (y-coordinates).
If you made a T chart like the picture you have above, you would have to put x (age of person) and y (books read).
So,
x = age of person
y = books read
