A group of 28 screenwriters have filed a class action lawsuit against the major television networks, studios and talent agencies, claiming that a pattern of age discrimination exists in the television industry that has squeezed out writers who are over 40. The writers charge that the networks, studios and agents are so eager to capture young audiences that they reject older writers with extensive experience under the assumption that younger writers are best suited to script programs featuring characters in their 20s and 30s.