Sex and health questions oh my...

Newbie with a couple of questions. Pix are attached. I'm trying to figure out the sex of my plants. They are between 30-50 days old and are starting to show preflowers (I think). there are some distinct differences but I need a little help recognizing what is what since I do not have balls sacks yet. Wait... I do but we're talking about my plants.

I've also got a little yellowing of the older leaves going on. I'm guessing they need a little more food but am hoping someone will recognize this and tell me what is going on.

One last thing. How tall do I want these guys to get before moving them into flowering? We're vegging now and about a foot tall on average. New set of leaves every day which is awesome.

Thanks. This is an extremely helpful site.

none of that are preflowers, in the middle pic, just stipules. 3rd pic actually looks like small nutrient burn maybe acidic ph. and 1st pic isnt pre flowers they are just branches, when you see flowers you will see a small egg looking thing that shoots out a small pistil, eventually forming the bud, males will have the same small egg looking sacks but will eventually look like sacks almost little balls hope this helps peace

hey bro your also look a bit stretched what is your lighting how are you growing soil nutes...?

Definitely stretched, need more light! there shouldn't be that much distant between the sets of leaves at this early stage in growth. Possibly lack of nitrogen, but you've got other issues to worry about like lighting, and it looks like they're in plastic cups, you need to get some decent sized pots to transplant them into. they look healthy as far as nutrients, but they're stretched. goodluck with the grow!

Thanks. First timer...

They are on a mixed diet of sky light and low wattage CFL. I was planning on getting 2 65W CFLs but have sort of been holding off due to the low opinion most people seem to have of CFLs. Local stores make putting together a HPS light sort of problematic.

Sounds like I need better light and less food. Good to know.