It’s Adar Sheini.
This leads to an interesting phenomenon that we’re experiencing right now. Since thirteen years ago was not a leap year, there are no Bar Mitzvahs this month. Everyone born in Sh’vat 5758 had their Bar Mitzvah last month and everyone born in Adar 5758 is having their Bar Mitzvah next month. So this month (Adar I 5771) there are no Bar Mitzvahs.
The Wolf