still in one's formative stages

formative years
〔人格の〕形成期、発育期

grammatical formative
《a ～》文法形式素

lexical formative
語彙形式素

organ-formative
器官形成の

in one's formative years
形成期に

professor of formative culture
表象文化論の教授

still in one's formative stages
《be ～》まだ初期の段階である