I just got back from a trip to Medellin where I stayed at two hostels and a friends home. The second night (and for several nights after) I stayed at Global Medellin Hostel. The staff was very friendly and it didn't feel like a hostel at all. All rooms are private and I don't know about the others, but mine was huge! 2 beds (private room), large bathroom, mini fridge, closet. Much more than I had expected.
The other patrons were older than I expected to see in a hostel, probably mid 30's, but I only met a few others.