bash-4.2$ mkdir dir{1..3}
bash-4.2$ touch -t 201211010000 dir{1..3}/file{1,2}
bash-4.2$ ls -l dir{1..3}
dir1:
total 0
-rw-r--r-- 1 sysadmin None 0 Nov  1 00:00 file1
-rw-r--r-- 1 sysadmin None 0 Nov  1 00:00 file2

dir2:
total 0
-rw-r--r-- 1 sysadmin None 0 Nov  1 00:00 file1
-rw-r--r-- 1 sysadmin None 0 Nov  1 00:00 file2

dir3:
total 0
-rw-r--r-- 1 sysadmin None 0 Nov  1 00:00 file1
-rw-r--r-- 1 sysadmin None 0 Nov  1 00:00 file2

_find_opts=( 
  -maxdepth 1 
  -mtime +31
  )
_dirs=( 
  dir1 
  dir2 
  dir3 
  )

for d in "${_dirs[@]}"; do
  eval "__find_$d=( $( find "$d" "${_find_opts[@]}" ) )"
done

for fd in ${!__find_*}; do
  eval "_files=( "\${$fd[@]}" )"
  printf 'files in %s:\n' "$fd"  
  for f in "${_files[@]}"; do
    printf '%s\n' "$f"
  done
done

files in __find_dir1:
dir1/file1
dir1/file2
files in __find_dir2:
dir2/file1
dir2/file2
files in __find_dir3:
dir3/file1
dir3/file2