I'm going to assume we're talking strictly anime here? If so, my 'first' 2D came a lot later on in my life than my first actual 2D crush <Which was either Terra or Celes from FFVI>...
If we're going by anime, which I didn't actually start watching wholeheartedly until about 5-6 years ago <after I had picked up and read four or five Manga series>, my first true 2D crush was Nobue Itoe; drunk-lolicon-'onee-chan' from popular loli anime, Ichigo Mashimaro.
This is, of course, if you also don't include characters from anime from when I didn't even know the difference between anime and any other cartoon. Like back when I watched Dragon Ball Z, or Sailor Moon absently, and had no idea they were from Japan. IF we include those, then perhaps my first 2D crush stretches even further back, to the lovely Sailor Mars...or perhaps a little further ahead with Sailor Uranus and Neptune...Eheh...