You probably can get a loan with only 6 months work and credit history, but you'll be sharing the risk with the lender , which means you'll be paying for it (higher interest and/or fees).
If it were me, and I was in your shoes once, I'd wait the 18 months, and try to increase my credit score even more. Listen to Dan about having 3 lines of credit, but optimally, you'll be better off if they are different TYPES of credit. For example, an auto loan, an installment loan, a bank credit card and a retail credit card are different types of credit.
I can send you some good information on credit and credit scores if you'd like. You're in a great position to keep your scores at the highest level possible if you know what you should be doing now and down the road.