Join the AAC, you be surprised of the opputunities open to you if you knuckle down, keep your head down and be a good soldier.
Imagine the conversation in the bank, Im 18, unemployed and need to borrow circa 70k to fund flight training!
Not a chance in hell at the moment, the banks are hardly lending to home owners with equity in their property.
Even if you did get the cash, how would you make the monthly payments, being a full time student with no income? and with no gaurentee of a job at the end!
Its possible to apply for aircrew with the AAC once in, the careers office should be able to give you more details on that.
Your 18, serve your time, enjoy it, save the pennies and review it all again in 5 years, you will be early 20s, with cash in the bank, sensible head on your shoulders, and armed forces on your CV.
Good luck