The Door in the Wall, Marguerite De Angeli, was 1950’s Newbery Award winner.
Wow, Newbery judges love books set in medieval times: The Door in the Wall; The Midwife’s Apprentice; Good Masters! Sweet Ladies! Voices from a Medieval Village; Crispin: The Cross of Lead; The Whipping Boy; and I am sure the list goes on, but I won’t.
A young boy is left behind—his mother goes off in service to the queen, his father to serve as a nobleman soldier with the king—to be sent off to the service of a nobleman, where his training for a future such as that is to begin. But it is not to be so for Robin! He becomes stricken with illness and finally taken under the care of a monk(s) who begin to show him that his new illness-induced crippling injuries shouldn’t stop him in his quest to rise to be a noble man.
Not my favorite, not the worst. Would I recommend it? Maybe, but there are much better books out there.
Age: Amazon lists 10+.