Wow, how time flies by. When I was sixteen, I was "sure" I would never have kids of my own. I was too enlightened for that - there were so many kids in the world already who needed love and a family, so I was going to adopt.
When I was eighteen, I added on the aspiration to join, and remain in, the military for twenty years and retire.
When I was nineteen, I met a guy who was "nice" and who made me laugh - he was the best friend of the guy I was dating at the time. He had always said he would "never" join the military, and especially not the Air Force.