Plant of the Year: 2014 - Plant of the Month: Dec 2014 - Nug of the Month: Feb 2015, Mar & Aug 2016, Dec 2017, Aug 2018, Jan 2019 - Nug of the Year: 2017 - Photo of the Month: June 2018
You're close to flip time.
If you're growing without training - just letting the plant grow naturally - you can count on it doubling or tripling in height before it stops. If you train for multiple tops, it may only double or less.
If it's 18" now, it'll be at least 36" before it stops stretching.