Mishne Berura, I believe, writes that a Bar Mitzvah seudah (meal) is conferred the status of a seudas mitzvah if either it is held on the day of the boy's becoming 13 (i.e. his birthday) or, he delivers a dvar Torah.
If it is not practical to celebrate the Bar Mitzvah seudah on the boy's birthday, may it be held earlier -- before the boy becomes 13 -- and have the status of a Seudas Bar Mitzva as long as the boy delivers a dvar Torah, or must it be held after his birthday since one can't celebrate an event that has not yet occurred?
Obviously, the aliyah laTorah and all activities that require one to be actually a Bar Mitzvah and obligated in mitzvos will be held after the boy becomes 13.
Please provide sources to Poskim in your answer.