There's a TED lecture about this (ted.com) that was done , they show and speak about the original marshmallow experiment, apparently, they followed up with the kids 14 years later and the kids who had controlled themselves and waited patiently for the second marshmallow were the kids who were doing great in college because they were future focused instead of present focused,and were delaying gratification by working hard presently for rewards later on. Fascinating stuff.
You don't 'become' a bar mitzvah, you HAVE a bar mitzvah.