You can't really over fed them, as long as you don't mess your water quality up. I keep some of my shrimps on a constant supply of live food to keep them entertained. Others we feed 3-6 times a day, some just once a day. They do get bored of old food and really like a change in diet from time to time. These shrimp have very strong chemosensory structures, so any food that has a lot of smell will get their attention. The only time you don't see them eating is right before and after a molt. Normally you can expect them to live about 2 years or so, maybe a bit more or less.