you can produce collostrum as early as 12 weeks....i'm 16.5 weeks and i've had it since about week 10. its just a hormonal response and your milk won't "come in" for many more months (usually right before the baby is born).
As to the milk, it does varie between woman when they do start having milk. Some have it early and some don't get it til their last month. My sister was 20 weeks when she was already lactating. She was also always leaking between 30-40 weeks.