Grandpa likes pencils but not pens
Grandpa likes Beijing but not Tokyo
Grandpa likes math but not chemistry
Grandpa likes Contact but not
Grandpa is old, and therefor only likes old things. Out of any two (similar) things he very much prefers the older one.
pencils have been around for a long time (they where charcoal sticks at some point), pens are a quite recent thing.
Beijing was founded ~1000BCE, Tokyo probably in the 14th century.
Mathematics was pretty much the first science developed by advanced. Human civilisation, chemistry (as science) only started in the middle ages
Contact is a movie starring Judie Foster from 1997, Flightplan is from 2005