Thanks for having a look - it didn't work. Also I need to introduce some set analysis and don't know where that would fit in this expression. I've used the if statement to get colours to change based on age of dates and that works fine but getting similar logic into an expression with set analysis is proving beyond me.
or use an appropriate date format code with Date() function as second argument. I assume you want to count records older than 30 days (which have a date numerical value lesser than today()-30, hence the smaller comparison)