Growing is learning to take on more and bigger problems. When you were a 4-year old kid, you basically had no problems, except maybe that you didn't feel like eating all those potatoes on your plate. Similarly, newborn open source projects have no problems either.
Once you start school, you might start to lose some sleep over your grades, whether you'll ever make your way through school or why you're not allowed to stay up a little longer at night. Remember how these used to be your biggest problems?
Later when you're done with school, you look back and you realize how ridiculous it was to even worry about your grades. If you'd have to go through school again, it would be the easiest thing on earth, you believe. However, you're now faced with new and seemingly bigger problems: will I ever find the right person to share my life with? How am I supposed to pay the rent? How to raise my kids? How am I going to cope with the loss of a close relative?
So growing is learning to deal with more and bigger challenges. It is no coincidence that the biggest challenges tend to be ahead of you. This is true for your personal life as well as for the life of an open source project.
Right now, Drupal's hardest challenge is to manage its explosive growth. We have raw and untampered ambition but we're left wondering how we can scale our infrastructure with the available resources, how we can attract more top-talent to help get all the work done, how to maintain — and raise — the high quality of our work, and how to make Drupal easier to work with. We're also learning how to deal with legal issues, we're figuring out how to better market ourselves, and how to efficiently organize large conferences.
This sounds a lot like "How will I be able to pay the rent?" (infrastructure) and "How can I score more girlfriends?" (more top-talent, easier to use, better marketing). So by that standard, Drupal is a young adult that just moved out from its parent's place. We have many new things to learn and to explore, but we have unlimited motivation and ambition.
I'm convinced that one day we'll look back and realize how ridiculously simple it was to scale our infrastructure, to organize a 400-attendee conference or to better market ourselves at drupal.org. After all, we no longer lose sleep over high-school problems either ...