I hate when people ask those types of questions, especially to parents of infants....*grr*
Anyway, there are a few options really, depending on who the person is and what bearing they have on your life...
To nosy or condescending people you could remark in a pleasant voice, "When? Oh, well, I guess when I'm d*mned well ready too and not a minute before." hmm, maybe a little too crass?
How about...When it becomes the most viable option for my family?
When he/she is old enough to express a desire to go.
Never. (Note the period at the end of that word...
)
I haven't decided yet, but seeing as how I'm the parent and this is my child, I'm sure its very much my perogative.