retics def grow faster, my male mainland i used to have hit 11ft in a year and 5 months while my 2 and a half year old female burm was only 8-9 ft. my female burm is now 12-13 foot at 6 years old and my 5 year old male burm is 8-9 ft, both are in 8'x3'x2' cages.
from my experience retics usually grow in length first then fatten up a bit. the retic would easily outgrow a 4x2x2 in a year, but it may be possible to keep a male burm in that for almost 2 years