Green House and Amity Poshtel are owned by the same group. Under 30s should consider staying at Amity Poshtel, just about 10 meters up the road. Amity seems to cater to the younger traveller.
Nothing wrong with Green House though. This is a cheap, safe, clean place I spent 6 nights at while exploring the area and using Krabi as a home base. Down the street from the hotel on the corner of the busy Maharaj Road street there is a restaurant that serves incredible steamed dumplings of all varieties for really cheap. Otherwise it's the night market about a 15 minute walk away. The hotel offers a standard western breakfast but you can go up the road to the restaurant on the corner for steamed dumplings for breakfast as well. You see a lot of Thais sitting there in the morning.
If you are in the area with some time, in front of the 711 down the Maharaj Road towards the night markets etc you can catch a white 'bus', a pickup truck with seats in the back, right by the 711. They take you to Ao Nang beach and back for 50 or 60 baht each direction and run every 30 minutes or so all day until about 6.30 pm.
Once at Ao Nang beach, after you explore that area you HAVE TO take a long boat around the peninsula to Railey Beach. That costs 200 baht return. Everyone agrees that it is the most incredible beach in all of Asia. The west facing one. The other options on Railey are all within about a 20 minute walk. Go to RAILEY!