Wow, that sounds really impressive a way to get started.
So is your motivation to achieve the end result, or to write a mostly arbitrary script file?
For the end result, there are a fair few scripts around for Nagios, e.g. http://exchange.nagios.org/directory...-Check/details
Note that Nagios scripts will work locally or remotely, you just need to run them via another remote check script, e.g. check_ssh or check_nrpe (i really dislike nrpe though...)
For learning... well here's a bash script doign mostly what you're after - http://www.noah.org/wiki/Test_file_age
and from the way you talk, I'd think that as long as you take the time to understand what's going on you'll be fine. This solution doesn't use find though, so if you do want to use find, which is also a very legit way to do it, you'd want to use the -mtime option and check the exit code of find after it's completed (echo $?) as one way to work out a success or failure.