There are several posts regarding to this. It depends on the breed, if you get production breeds, anywhere from four to six months of age they will start laying. If heritage breeds, anywhere from six months to a year.
Production hens, live to be two to four years, with exceptions they live past that age. Many of them succumed to egg laying diseases.
Heritage hens, live anywhere from four to ten years. Not as many problems as egg production diseases but they will stick around alot longer than the production breeds.
Ditto what ewesheep said. I tend toward dual purpose birds that give a moderate number of eggs rather than high production birds that burn out early. I have one 10 year old New Hampshire hen that was giving me a very large egg every other day this spring. Then I moved 50 chicks into the coop and she went broody, nesting on the floor with them at night and cuddling as many as she could. I suspect she'll lay a few more once the 'kids' are past their childhood.