After winning his first NBA title at 38 years old, Al Horford plans to return to the Boston Celtics next season, Celtics owner Wyc Grousbeck said Tuesday. “Al is coming back for next year. That’s what I’ve been told. Age 38, which is unbelievable,” Grousbeck said on the “The Greg Hill Show” following the Celtics’ championship-clinching Game 5 win Monday over the Dallas Mavericks.