Everything about Mark Morris is big: his exuberant laugh, his passion for music, the uncensored chat and bawdy talk, his endlessly inquiring nature. He’s a stayer, too. The American choreographer started making dances when he was 13 (although he says he didn’t make his first good one until he was 15) and founded his own company at 24. He’s now 58 and Mark Morris Dance Group has not only survived, but is one of the world’s finest contemporary companies.