I love bananas, and could probably eat the ones from 4 to 10. On the greener side, basically as long as I can easily peel it, it's edible. On the riper sider, once it gets mushy, it becomes muffins or loaves.
1 or 2. I'm not a banana fan overall, and, once they start to get even a little ripe, I'm done with them. I don't care for banana bread either.
One time I walked into my boss's office and he was eating a banana that I'd say was probably in the 20s. The thing was black. I didn't say a word. Just asked my question, got my answer, and left. Later on I got a phone call, "I take it you didn't like my banana!" "I didn't say a word!" "You didn't have to say anything; your face said it all!" Well, it was completely disgusting.
Anything from 6-10, but 13-15 for banana bread. I'm not really a big fan of banana on its own and only like it in things, so am basing 6-10 on what I've given the young children I used to work with at my old job in a pre school!