Database cleanup - determine which databases have been inactive

Hi All, 

I was asked to perform a cleanup in a couple of our SQL servers. I need to determine which databases have been inactive for let's say more than 4 months. Then I would have to put them offline. I am not an expert in SQL scripts, therefore I need to know if any of you have one of those handy. I also thought that by checking the 'Date Modified' column in the DATA folder I would be able to know which .mdf files have been used for that time period.

Any ideas?

Thanks in advance, 

AOS