*UnitedHealth lowers 2013 revenue outlook. April 18- Lower government payments for private Medicare services and prescriptions for older people dragged down UnitedHealth Group Inc's first-quarter profits, the company said on Thursday.
Jan 17- UnitedHealth Group Inc, the largest U.S. health insurer, reported a slight drop in fourth-quarter profit on Thursday as medical costs rose, but revenue increased more than 11 percent, helped by growth in its Medicare, care management, technology and international businesses.