I'm 23 weeks and my nipples don't leak at all. Yet if I massage or squeeze my nipple only a little will come out. After I gave birth to my first child my breasts were leaking milk and I was able to start breast feeding him in the hospital. So it all depends.
You usually won't leak only colostrum will come in my milk didn't come in till 3 days after my baby was born but don't worry they get the colostrum and that's what they need when they are first born.
Like they always say, every pregnancy is different. My 1st pregnancy I had to wear breast pads 20 weeks on. This time at nearly 24 weeks I have only seen leaking if I bumped into something (I'm pretty clumsy)
It just depends on the baby and your hormones and time. Try not to worry
Colostrum can come during pregnancy, but doesn't always. Milk comes in a couple of days after birth, the vast majority of the time.