See attached. I have created 2 variables - vLastYear (today last year) and vMonthDiff (months between today and first transaction date). Using a combination of set analysis and RangeMin() you can achieve what you wanted.
Thanks must go to Rob Wunderlich for his MonthDiff solution (http://community.qlik.com/thread/47580?start=0&tstart=0)
Hope this helps,
Community_51993.qvw 153.8 K