IIRC, it’s about a rov who convinced an elderly man to start
putting on tefillin. He told him that the posuk says that our
lives are 70 years (“y’mei sh’noseinu shiv’im shana”), and so
83 could be considered a second bar mitzvah for 13 years of a
second lifespan. Therefore, it would be fitting for him (late 82)
to start putting on tefillin as a boy does when he’s approaching
bar mitzvah, and if he would do so, the rov would make him a bar
mitzvah seudah when he became 83. And so it happened.
(I don’t remember where I read the story, but it was probably
in a volume of Visions of Greatness or of the Maggid series.)