Very often the emperor was only a minor, so that the Fujiwara patriarch acted as regent.
( Very ( ( often ( the emperor ) ) ( ( ( ( was ( only ( a minor ) ) ) , ) ( so ( that ( ( the ( Fujiwara patriarch ) ) ( acted ( as regent ) ) ) ) ) ) . ) ) )
(ROOT (S (ADVP (RB Very)) (NP (RB often) (DT the) (NN emperor)) (VP (VBD was) (NP (RB only) (DT a) (JJ minor)) (, ,) (SBAR (RB so) (IN that) (S (NP (DT the) (NNP Fujiwara) (NN patriarch)) (VP (VBD acted) (PP (IN as) (NP (NN regent))))))) (. .)))
Sometimes the emperor was less than 18 years of age. 
( Sometimes ( ( the emperor ) ( ( was ( ( ( less ( than 18 ) ) years ) ( of age ) ) ) . ) ) )
(ROOT (S (ADVP (RB Sometimes)) (NP (DT the) (NN emperor)) (VP (VBD was) (NP (NP (QP (JJR less) (IN than) (CD 18)) (NNS years)) (PP (IN of) (NP (NN age))))) (. .)))