Jason Biggs -- My Dog Just Became a Man

Jason Biggs better learn the horah ... 'cause his dog turned 13 Thursday -- and his wife threw the cute pooch its own "bark mitzvah" to celebrate.

Like a true yenta ... Jason's wife Jenny Mollen documented the whole ceremony on her Instagram when she and Biggs took the dog -- named Teets -- to a temple to make things official.

The whole fam dined on challah afterward to commemorate the special day.