Wow, I love all you posters! I second so many suggestions. Thrilled that your DS has read Terry Pratchett (my fav author) and Tolkein!
So many great authors mentioned: Brandon Sanderson (Reckoners and Mistborn series), Nevil Shute, Agatha Christie, Robert Heinlein, Neil Gaiman, Jerome K Jerome, Jasper Fforde, David Eddings, Diana Wynne Jones(!!) and many more...
Some other suggestions:
DL Gardner - Thread of a Spider (Irish History mixed with Irish Folklore)
Jonathan Moeller - Frostborn Series (Fantasy like LOTR). Main Character fights with a staff. Great cast of characters.
Sheri Cobb South - John Pickett Mysteries (JP is a young Bow Street Runner. Great if he likes mysteries. Start with Pickpocket's Apprentice)
Baroness Orczy - The Scarlet Pimpernel (Love that it was the precursor to many of the masked hero type stories)
TH White - The Once and Future King
Kevin Hearne - The Iron Druid series ( He will laugh through it, the dog is wonderful!)
John Buchan - Richard Hannay Series (starts with The 39 Steps)
Margery Allingham - Campion mystery series
Edward Marston - Railway Detective
PG Wodehouse - everything
Marian Babson - Nine Lives to Murder and the Perkins and Tate mysteries.
Connie Willis - To Say Nothing of the Dog, Bellwether and Blackout/All Clear
David Weber - Honor Harrington series (another outer space series)
Tanya Huff - Confederation Series (there is the mention of people going off to have sex, but it is never described, or actually happening in the story. There is profanity though. Stories are outer space. Main character Torin is amazing)
Apologies for the long post. I love readers!