Mailing list using previous purchase date

[Jesse Aiken]

I'm working on getting a property list from the county to scrub and create a mailing list. I'm unable to specify an equity amount to pre-filter the list through the assessment office, so I plan to filter by last purchase date. I'm curious if anyone has a rule of thumb to use for a minimum number of years from last purchase date? For example: last purchase date 10 years ago or more? I want there to be a better chance that I'm marketing to owners that have equity.