Lamb comes from a sheep that is under a year old, and often as young as five to seven months. Special varieties include baby or hothouse lamb, which is only six to 10 weeks old, and the meat of lambs raised in salt marshes, which has an unmistakably briny tang. Mutton, on the other hand, comes from sheep older than one year, and it has a more robust taste. Here are some benefits of adding lamb to your dinner table and some tips on how to prepare and portion it.