To join the AAC you don't have to be a soldier first. They take direct from RMAS. If you want to join from the ranks then yes you do have to do a couple of years soldiering but it doesn't have to be in the inf.
"Soldier First" is an ethos, not a qualification. It simply means that whatever you might do for your shilling while serving with Aviation, you are always expected to be a professional soldier first, commissioned or enlisted. Operating the Apache has driven this point home more than any vague doctrinal fluff ever could.