My son's first word (and currently his only word) was ball. He's been babbling dada and mama and nana and gaga for months on end, but when he finally wanted to actually say something, he said the one thing that really moves him: ball.
Incidentally, he also walked at 11 months, which was amazing. I was so proud of him for getting so mobile, so fast. But while other moms talked about their dear ones finally taking those independent steps beyond walking from/to mom and dad, I was sitting there thinking of all the times I put my arms out for him while he chose to just stand there waiting for me to come to him or maybe drop to his knees and crawl to mommy. It was a big red ball that motivated those legs to get steady, not me.
So, I have to think that if I asked the little guy what he wants to be when he grows up, his answer would simply be: ball.