on average, sure, but lots of overlap.
you can put them in flower to see and then re-vege, which takes forever.
You can see preflowers if they vege long enough, but this may be way too large of resulting plant in most cases.
you could grow some out outdoors, then take clones for use when you know gender
You could also take clones and put rooted clones into flower to see, which avoids re-vege for your plants, but that may end up taking as long as it would take to see preflowers.
The incremental difference between fem and regs is not worth the effort, imo.
Pay 10-20/pop to get gender testing done at a local lab. You send in a tissue culture and get back an answer fairly fast.
Buy a mini-PCR and bits and do the genetic testing yourself... 500-700 startup cost. The instructions are something you can look up.. not a problem. Could charge others to recoup costs.
theoretical -- may cause it to herm or something, lol... Plants are fairly compartmentalized in that they react to environment. So, cover up a useless branch so it is dark 12hours/day and that 1 branch will start to flower... will that also fuck up the hormonal balance in the plant while doing so? Maybe. This will work as far as displaying gender, but no idea if it's going to cause major problems, like herming.