This is using find and -mtime in Centos Linux, it simply takes "n" (which is a day) as a number and you can specifiy a + or - to say older or less than a certain age.
# (show everything older than 1 day)
find . -mtime +1
........
sed is the easiest way and you just specifiy the line number with the "-n #p" file.txt
So for example below 2p means print the second line of names.txt
sed -n 2p names.txt
What Are you Looking At, Mr. Bear?........