If-
Not familiar with CDG
No elite status
Bags couldn't be checked through


Then-
I'd recommend arrival at CDG a ridiculous 3 hours prior to flight. If Star Alliance, final security will be at the gate, which you'll want to be at an hour prior to flight. Can't speak for other alliances.


Else-
Two hours prior to flight OK if you could tick off all three checkboxes, or at least that your bags had been checked through.


If you can figure a way to work in Gare Nord as a destination, then you can catch a train straight to the airport (44-48 minutes if I recall correctly). The Eiffel Tower opens at 9am; you might consider doing just that one thing, since it's the ultimate Parisian Icon to young adults (and maybe everyone else too), and head straight to the airport afterward. If you get up and back down in an hour, you could walk to the Arc d'Triomphe and head to the airport from there. Google maps can give you the details for the metro and trains.

Or perhaps get a hotel near the Arc d'Triomphe and head out at 7:30am or so on foot for breakfast and the Eiffel Tower, and head from there to the airport.

All of this assumes you meet the criteria for arriving at the airport just two hours prior to departure. If you need three, that makes things pretty tough. Basically just breakfast and the Eiffel Tower. Still, you'll have been to Paris!