True, you can only have two pops at the aptitude, but once you have passed, you can keep going back until the cows come home and they'll take your highest score from the first two attempts each and every time.
Have a little inside knowledge as to a good aptitude score, and without trying to dishearten you, 140 is what you need to aim for this year to be competetive.
Like yourself, I went for pilot aged 18 and was offered AEOp (forerunner to WSOp) and took it. I certainly haven't looked back and have had an absolute blast. Time to move on though, and this year sees my 5th attendace of OASC for pilot application (think they're trying to tell me something).
Whatever you are offered, take it. No need to cut your nose off to spite your face as my mother once told me. Sitting in the back of the mighty hunter is not as bad as some people make out.
Always on the end of my PM's if you need any more advice.
Good luck.