Apple script to purge downloads, this can be easily set up in automator to run every day.

Purge Downloads

-- number of days until purge.
set modDate to (60)
	
-- Only do for the current user.
tell application "System Events"
	set currentUser to (name of current user)
end tell
	
-- Delete
tell application "Finder"
	try
		delete (every item of folder "Downloads" of folder currentUser of folder "Users" of startup disk whose modification date is less than ((current date)) - modDate * days)
	end try
	
end tell