After three decades at LA firm Altoon + Porter, founding partner James F. Porter is leaving to become a principal at the Jerde Partnership. Porter, who met business partner Ron Altoon while working at Frank Gehry’s office in the ’70s, co-founded Altoon + Porter in 1984. Hoping to leave more room for young partners, Altoon + Porter included a clause in their partnership specifying that they retire at age 65. “Sixty five came along in a nanosecond,” said Porter, who managed to adjust the agreement to stay on a little longer. But at age 70, it was time to go, he said.