Here is how to create a date in the last 10 years:
rand(10.years).seconds.ago
You can also get a date in the future:
rand(10.years).seconds.from_now
Older versions of Rails (< 4.1)
Prior to Rails 4.1, there was an implicit conversion from Numeric => seconds when you call .ago. See Rails PR #12389 for more information about this. So this approach is possible:
rand(10.years).ago
rand(10.years).from_now