When to force the flowering stage?

Hey, so I was wondering at what point of the plant's life should i begin the flowering period. The thing is that I want to begin as soon as possible, and I'm not aiming for the quantity at the end. My plant is about 30-40 days old and it's about 30cm in height. And also, if i begin flowering it at that age would it produce lower THC levels.

Thanks

you can flower anytime you want. but its best to let the plant mature meaning alternating nodes