When James MacArthur was 16, his Dad said, “You’re going to have to master the world’s toughest trick -- walking in the footsteps of famous parents. Don’t trip, boy.” Jamie hasn’t, but it wasn’t easy for the adopted son of actress Helen Hayes and late playwright Charles MacArthur. Born December 7, 1937, in Los Angeles, Jim graduated from Solebury, exclusive Eastern Prep School, “within an inch of being expelled until he declared a truce,” says his famous mother. “He’s a devil, but an adorable one.” After tiny roles in The Corn is Green and Life with Father, Jamie’s real debut came in The Young Stranger on TV. The amazingly gifted 5-foot-7, stocky youngster, with two films under his belt -- The Young Stranger and Light in the Forest -- found himself a fast-rising star and teenage idol. A student at Harvard in winter, a film star in summer, Jamie has blond hair and blue eyes. He is not what you’d call handsome, but his steady girl, Joyce Bulifant, doesn’t give a hoot, and is looking forward to their marriage.