I don't think that you can type in an address for location-based reminders. I believe you have to select a location from your address book.
A number of people in other threads have noted this as an issue and I have to agree.
The "workaround", if you can call it that, is to locate the location you want on the Maps app, add it to your address book, and then select that newly added location from within the Reminders app.