I once heard there is an opinion in Rishonim (maybe Gaonim?) that says we count ones years of life according to the solar calender. So for example a boy would become bar mitzvah when he would turn 13 ...
What sources are there for our minhag of doing a Bar Mitzva Seuda (meal), and do the sources state that the seuda must specifically be done on the day of the Bar Mitzva (or the night of)? And is this ...
How do we know that a person is not obligated in Mitzvos before the age of 13, and is obligated from that point forward?