I probably would start to flower those now, but it all depends on how much room you have vertically. The longer you veg them the bigger they will be and the more buds you will get.
You will see signs of sexing in about 1week to two depending. If you notice these balls(clusters) or banana shape things, it is a male and get rid of them! No bud will be produced from a male just pollen sacks.
How old are they? you can throw plants into flowering after like 4 weeks, but you will not get as much growing in soil. Hydro, is awhole other thing which I am reading up on daily. So much but will be worth every word read and dollar spent.