I am suppose to do a cake for Friday noon. It is a for a girl turning 16 and a boy turning 17. She will be getting her beginners to drive and he's into astronomy,now how do I incorporate these 2 into one cake that is suppose to serve 15 people? Any ideas would help.

Figures on top of cake. Car has to be convertable - She driving, hair flying car tilting to look just slightly out of control. Maybe an instructor in the passenger seat with clipboard looking a little scared. Brother looking out the back of the car with a telescope, not seeming to notice the car is out of control.

Drivers license with a constellation surrounding it. You could put stars of constellations on the side of the cake too.

I'd go w/a 2 layer 8" round. Have cars driving around the bottom w/driver as described above. If possible I'd use frosting sheet pix.
On the top I'd put a telescope and stars (on wires?).
Maybe the message can come from the car's exhaust? (In white puffy dots)

What about a topsy turvey cake with the crazy driver and car and the constellations surrounding the cake or maybe their birth signs? Perhaps having "her" driving the Columbia and "him" looking out or in a astronaut suit?

A car driving on the Milky Way?

uuuhh, maybe not the Columbia....

A 9x13 cake is enough to feed 15.
I'm thinking of the "Back to the Future" car/time machine.
Draw that car going into a midnight sky with stars. The words can be from the movie: "Roads? Where we're going we don't need roads."