She was pretty enough, in an innocent sort of way with those round cheeks and big eyes, although that girlish hairdo of twin buns only solidified the fact she probably hadn't reached Majority yet. Her actions, her personality, that brief feel of her body as he'd hoisted her above the garbage heap in the Death Star, however, left no doubt she was all woman. It was enough to pique his curiosity despite common sense and bigger priorities.
Ironic how Luke's reverential attitude died the more he knew her in the flesh, while his own ascended with each encounter. A princess.