Can plants show sex before going 12/12?

[canadagrown]

As stated in title. I have a bunch of plants and would like to know sex before starting to flower since space is limited. The guy at the grow shop said you can only tell sex after starting to flower. Please clarify guys. Thanks.

[redtails]

You either force flowering until they show sex and throw them back into veg or you can top them and root that as a clone then flower the clone. Or if you wait they should show sex with preflowers after a month or two depending on strain.