"Is there a way to find out when a stored procedure was last updated?"
SQL stores the date the Sproc was created but not when it was updated
If you always use DROP PROCEDURE ... CREATE PROCEDURE ... you can use that date. However, if you use ALTER PROCEDURE ... you can't
We have an SProc call at the top of all our scripts that "logs" the fact that that script was run, and this allows us to see the dates when we ran a particular script (it also logs the "version number" of that script).
We store each Stored Procedure in a separate file, so in effect we get a LOG of whenever each Sproc is updated.