Lose the weight - your chances of crossing over will be slim. Boom Boom
You'll fail the fitness test at AIB whether it's Pilot or Wafare you want - the test is the same for both, though the medical is tougher for aircrew.
Quite how you've got so lardy at 18 is worrying though - when was the last time you stepped away from the PC/TV/Playstation? It may suggest that there's more you need to do than just lose weight if you are to impress the AIB.