I got my first one as a girl scout, I think I was in 6th grade. I couldn't let him be lonely, so begged my mom for a second one. As it turns out, they are quite social animals (at least the ones I've had) and I often heard them chirping to each other. Mine never pinched me, but then I also handled them all the time. I had them out of their cages a lot, and they interacted with my cats too.
I am not sure about average life span, but those 2 hermit crabs lived at least 8 years - as they went with me to college! Fun creatures, and even more fun when you give them stimulation in their own environment. I always enjoyed giving them different pieces of food to see what they liked and didn't like. Lots of things for them to climb and crawl under. Mine were also diggers, and really really loved it when I replaced the standard fish gravel with real sand.
My son has been begging me for another critter (we already have 4 cats and 2 big dogs at home!) and this is the only one I think I'd consider.
“Riding a horse is not a gentle hobby, to be picked up and laid down like a game of Solitaire. It is a grand passion.” ~Emerson