Combining knowledge of users with ratings

Hello, I am new to Mahout but not ML in general

I want to create a Recommender that combines things I know about Users with
their Ratings.

For example, perhaps I know the sex, age and nationality of my users. I'd
like to use that information to improve the recommendations.

How is this information represented in the Mahout API? I have not been
able to find any documentation or examples about this.

Thanks
Peter