I've done a little more thinking about the
reading thing. Reading requires a willingness to be open....
to ideas-experiences, sometimes worlds...
that does take a certain amount of energy...
Sometimes that type of exploring is more often done in one's youth....
He is your younger brother but is not young anymore.(trust me I know I would love to be either of your ages....:) but from the words you relayed he sounds tired with a sense of time &energy limits.
I wouldn't take it as a real comment on reading, Pratchett or your obvious
affection. Sounds like your little brother has a tiring life.
LTA