Courtney Sullivan starts Monday as director of the Walpole Council on Aging. She replaces Barbara Coghlan, who retired in January after more than 30 years on the job. Sullivan was chosen from eight candidates, according to Assistant Town Manager James Johnson. A Bridgewater resident, she is currently a program manager at Linden Ponds retirement community in Hingham, where she has worked since 2006. Sullivan will earn $63,181 in her new position.