Created or last accessed? Created will be impossible since inodes don't store file reation time, just access time, modification time, and status change time. Read the man page to find, something like:
find . -mtime +10 -mtime -20
will print out a list of files modified between 10 and twenty days ago; add the appropriate -exec switch to remove them (be careful it's working right before doing this!) and you're set.
 Status change time is often the creation time, but it can't be relied on.