The Knicks are getting older on the court but younger in the broadcast booth. Knicks legendary broadcaster John Andariese, a team radio staple for 40 years known around the Garden as “Johnny Hoops,’’ has stepped down from his color analyst position, the Knicks announced Friday. Andariese called the Knicks’ last championship — in 1973 with Marv Albert. Andariese will be replaced by Hubie Brown’s son, Brendan Brown. The Knicks had reduced Andariese’s role last season, having him do just home games.