Repository Methods vs. Extending IQueryable

I have repositories (e.g. ContactRepository, UserRepository and so forth) which encapsulate data access to the domain model.

When I was looking at searching for data, e.g.

• finding a contact whose first name starts with XYZ

• a contact whose birthday is after 1960

  (etc),

I started implementing repository methods such as FirstNameStartsWith(string prefix) and YoungerThanBirthYear(int year), basically following the many examples out there.

Then I hit a problem - what if I have to combine multiple searches? Each of my repository search methods, such as above, only return a finite set of actual domain objects. In search for a better way, I started writing extension methods on IQueryable<T>, e.g. this:

public static IQueryable<Contact> FirstNameStartsWith(
               this IQueryable<Contact> contacts, String prefix)
{
    return contacts.Where(
        contact => contact.FirstName.StartsWith(prefix));
}        

Now I can do things such as

ContactRepository.GetAll().FirstNameStartsWith("tex").YoungerThanBirthYear(1960);

However, I found myself writing extension methods (and inventing crazy classes such as ContactsQueryableExtensions all over, and I lose the "nice grouping" by having everything in the appropriate repository.

Is this really the way to do it, or is there a better way to achieve the same goal?