New grow share

I have recently started growing for the first time since I was a teen. So I started with a Big Bud Strain to see how my skills are holding up. I am aprox. 6 weeks in the veg stage. I have 5 plants. As of today I have one plant at 39cm tall, one at 20cm, two at 19cm and one at 16cm. I am not sure why they are growing this way. One was very unhealthy and I pruned to much but it is making a come back. My runt is catching up and my number one is amazing. I have had no serious problems and I am looking forward to flowering them. I am going to try and hold out till the end of july to do so. Does anybody know how tall they should be before I flower them? I thought at 8-12 weeks. But not sure. still trying to upload some photos. will keep every posted. Any tips would help as well.