Aidan,
A Quick tip. Although there are numbers that are not valid in dates like the 99th of the month, all date serial numbers are just numbers. It is quite easy to list items with a prefix of YYYYMMDD as an example. If you are gentrating such dates ensure each has a leading zero YYYY0MM0DD
The reveal widget allows for > < and = comparisons as do other calc or formula plugins.
However If you want to design something relative to today have a look at the days operator which has a form of > = < test built in.
In your example in the tiddler banking you could use the created date to feed into a days operator to list all (filtered items) with an older created date using the days filter.
Note: The Trick with the days filter is it is relative to the key date do -7 days lists dates from -7 through to 0 and forward, where +7 lists dates 7 days in the future through 0 and into the past. Two can be combined to get exact periods.
Regards
Tony