The last time I saw Gustavo Dudamel conduct at Birmingham’s Symphony Hall was in August 2005, when he stood in for an indisposed Neeme Järvi, at the age of 24. It’s astonishing quite how much Dudamel’s star has skyrocketed since then: he’s the closest thing the classical music industry has now to a global superstar conductor, and there was a packed hall in Birmingham delighted to welcome him back.