Ramifications of Jewish Leap Years

This year we are in the middle of a Shana Meuberet - a Jewish Leap Year. A Jewish leap year doesn't just have an extra day every 4 years it has a whole extra month every 3 years. Or to be more precise 7 times every 19 years. There are two months of Adar. With Purim celebrated in the 2nd Adar since there has to be 30 days between Purim and Pesach.

A person born on a gregorian leap year (February 29th) can celebrate their birthday on either February 28th or March 1st. But in our calendar with a whole month difference the question arises in a which Adar do we celebrate birthdays on? Adar Aleph or Adar Sheni? On which month are Bar and Bat Mitzvahs celebrated? On which month are meldado/yarhrtzeits commemorated?

I'm personally interested in the question as I was born in a regular year. Do I celebrate in Adar RIshon, Adar Sheni or both? According to most halakhic authorities you can celebrate both dates in Adar although some say just Adar Bet. For someone born in a leap year E.g. 12th  of Adar Sheni they would celebrate their birthday on the 12th of a regular Adar in a non-leap year. My Hebrew birthday is today 23rd Adar Rishon and in case you miss it, it's also on 23rd Adar Sheni.

But the real question is not birthdays but Bar and Bat Mitzvahs. At what age are they halakhically considered adult men and women and obligated in Mtzva observance? At what date does a boy count for a minyan? 

There are three possible scenarios:-

1. A boy is born in a leap year and has his bar mitzva in a non-leap year. 
2. A boy is born in a leap year and has his bar mitzva in a leap year.
3. A boy is born in a regular year and his bar mitzva is in a leap year.

For the first scenario E.g. his birthdate is the 23rd of Adar Sheni he celebrates his bar mitzva on the Shabbat following the 23rd of the regular Adar.

For the second scenario E.g. his birthdate is the 23rd of Adar Sheni 5755 he celebrates his bar mitzva on the Shabbat after the 23rd of Adar Sheni in 5768.

In the third scenario of a regular year into a leap year which was my bar mitzva, the halakha follows that the barmitzva is celebrated in Adar Bet. 

(For those interested in seeing the halakha inside see Shulkhan Arukh O.C. 55:10 Maran and Rema there)

For Meldados and Yahrtzeits the Sephardic custom based on Maran is to commemorate on Adar Sheni whereas the Ashkenazic custom is to commemorate Adar Rishon. The Vilna Gaon holds that one should commemorate in both Adars. (For more information see Shulkhan Arukh O.C. 568:7 Maran and Rema there as well as this very good piece on VBM.

The custom at SBH is if the person passed away in Adar Rishon the Meldado is in Adar RIshon but if a person passed a way in a regular Adar the meldado is commemorated in Adar Sheni of a leap year. Which is why this past month there have been very few meldados.