Well you are trying it in a wrong way. You have mixed two criteria into one. First, you need to list down the directories with name starting with A. Then you need to find out the files on each of these directories.
Here you go:
find . -maxdepth 1 -type d -name "A*" -print | while read dir; do find $dir -type f -mtime +10 >>/tmp/report; done
The list of files according to your criteria gets stored in a file called report in /tmp directory.