The boy was about six, and he had some speech difficulties.

Probably stammering. (It was later dicovered of course that he was mentally retarded.)
Whether Jane met him as young is doubtful. He was one of the first pupils that came to Steventon in 1773. And Mrs Austen writes in a letter the same year that "he has left us".
His father had taken him to London to see a specialist for his problem, so it's unclear if he returned.
Later while he was still reasonably sane he always(or it may have been his wife) invited the Austens to Hurstbourne Park,to the yearly ball on the anniversary of their marriage.

Leif Gn