I would second Davis' idea on a 1.8 190E as I believe this car to be a classic for younger people. The W123 model would prove a little too classic for a young adult as it might attract the wrong kinda attention, and being 5'4" might be intimidated with the sheer size and built of a W123. Besides the 190E certainly looks sporty and trendy (if well maintained).
If I had a daughter turning 18, I would think of a 1.8 190E. A baby Benz for my lovely Baby gal.
Too bad, with my 5'11" frame and a highly potential beer belly, I wont be able to consider a 1.8 190E for my stable!