I would not force them too young but in my Silver river video was no way near showing a bloom bud . Even though topped without the bloom bud showing the leaves will still color cure with top leaves being darker in color .
Topping before bloom bud shows will allow the leaves to grow larger . I like to top all my tobacco in early bud stage , Ct Broad leaf , Pa Wrapper , Maryland , Burley , Bright leaf , Havana , Bursa , etc.
My son is 6'2" , tobacco topped is right at shoulders or arm pits . On down the rows some plants in about 30 section of those rows was around two foot shorter than what he was cutting but produced the same quality tobacco .
In cold location / freezing temperatures it is best to keep green tobacco in a place where it won't freeze after you hang the stalks or leaves . I had some a couple of years ago and after it freezes while still green / yellow it will look like you have spilled oil on the leaves and will not cure out right . I still have some of that tobacco around , if anyone wants a picture of it .
My best field of burley , we topped it without any blooms showing . The plants may be bigger in parts of the field while shorter in small section of the field . Topping the entire field at the same time was best
This years tobacco was really weedy because of the rain . We could not get in our field to work . Plus growing organic I used composted cow manure and leftover un eaten hay that contained some weeds . This seeded my organic field and caused more weeds than usual .
The tobacco on the right is yellow twist . I didn't have time to top some of it and it still shows full bloom .
https://www.youtube.com/watch?v=uZ7A9Pft-G4