After 25 years as the founding artistic director of the Nora Theatre Company in Cambridge, Mary C. Huntington is stepping down. “Over the last few years I’ve found myself pulled by some different interests,’’ said Huntington, 60. “The theater has matured and it’s in a good place now. I figured if I’m going to make a change I should do it now. I’m not getting any younger.’’ Catherine Carr Kelly, executive director of Central Square Theater, where the Nora is based, said the hope is to find Huntington’s successor by September through a national search. Huntington will serve on the search committee and said she will continue as artistic director until her successor is chosen. During her tenure, which has included eight world premieres, Huntington aimed to stage at least one play per season focusing on women’s concerns and experiences, and to champion female playwrights and directors. Huntington founded the Nora Theatre Company in 1988 with Eric C. Engel, now the artistic director at Gloucester Stage Company, and Francine Beth Ferraro.