As far as I know - spraying is usually associated with either a medical problem like urinary tract infection which is treatable with antibiotic or behavioral/territorial due to too many cats or cats that are not neutered. Having one male kitten - having him neutered..I would say the chances of having him spray would be extremely slim.
Gus looks and sounds like a real sweety and if your Grandpa really wants a kitty - this fella might be the purrfect companion for him!