I'm in the same age range as you are...except I'm a bit more than 21.5, but not 22 yet. :P
I'm definitely planning on keeping the 335i for years to come, unless it really gives me major problems. I plan on buying a house or condo of my own before I upgrade to a better car. My parents are about to buy a new townhouse...only 1600 sq ft and it runs a little more than $600,000. Honestly I'd be happy to downgrade from a BMW to say a Toyota as well, as long as if I can have a nice house of my own. I'd rather have that than live at my parents' house at the age of 30 and drive an M5, lol.