Black wolf,
Seems that your parents are the intransigent, zealot type. Is there an elder or ministerial servant that is well respected and reasonable regarding your problem. Some JW's understand and are more patient. Sounds crazy, but you may get an ally in the congregation that may be able to placate your parents.
"I am not ready" is a good answer and a reasonable JW could help you keep your parents off your case for a while. I have known some JW's who understand quite well the statement "I am not ready"