Reference the Alpha Software Message Board, Advanced Search area, Additional Options area, Find Posts Row.
This row allows user to filter a search by selecting a length of time to look back to and fetch all posts newer than that date. The maximum value is "a year ago".
I would ask that additional choices be offered such as 2 years, 3 years, 5 years or allow the user to input the number of years.
Even though the software is constantly evolving it is valuable to have all the posts there because sometimes they are still relevant.