This is common problem with forums and websites where content is dated. If you are new to the forum or content area and you see a post dated 2007, people don't bother to read them as they think it is no longer relevant to their "new" problem. Look at the stickys on any page, the vast majority are quite old but still very useful today and should be read.
One of the ways we are addressing this in work is to change the dates on the posts to show when they were last revised (Checked) rather than when they were created. It is definitely work for the website team but we do it on a a rolling basis so that each section is updated\refreshed on a schedule that doesn't overburden the website team. For instance Tax, Banking, credit Cards are updated in January, Credit Unions, Investments, Alternative investments are done in February etc.
For general searching, perhaps it is possibly to change the default value to be todays date - 5 years ago - and then insert an note that the date value can be changed...
The above are just nice to have's, I haven't noticed the problem myself.