How could you start an essay about what you think it means to be an adult in an interesting way? create a couple sentences that you could use to gain the reader’s interest.

You could pose questions ...

"What does it mean to be an adult? Is it based on age? Is it based on employment? Is it a gut feeling? More important perhaps than these questions, is how the sense of being an adult helps one assume a larger role in our society."

I'm not sure exactly how you plan to go about your paper or what ideas you are exploring within your writing, so this might not work entirely. Nevertheless, I think it could be a good place for you to start.