Sexing your plants

So I have always bought fem seed but acquired some regular ones and wondered if I could tell the sex before I put them in flower. I have had plants show their pre flowers but only after cloning a few times. All 4 of my Super skunk fems are showing pre flowers and were started from seed on 1/21 so roughly 7 weeks from seed. If I let my others go this long will every plant eventually show pre flowers before flowering? Whats everyone elses method for sexing plants?

you can sex them by seed although this method is not the most reliable