You correctly found the mean age of the data set for the 10 a.m time in the library. However, the mean age of the data set for the 6 p.m. time is about 23, so there would probably be newer drivers in the library at this time. Also, the mean or average could be misleading. There could be many people who are old and many who are young, with an average age around 20, for example, without anyone being around the age of 20.