We don't have synonyms for outgrown yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are outgrow, outgrowth and nutbrown.
(v) :
(transitive, often figurative) To become too big in size or too mature in age or outlook to continue to want, need, use, experience, or accept some object, practice, condition, belief, etc.
(v) :
(transitive, often figurative) To become too big in size or too mature in age or outlook to continue to want, need, use, experience, or accept some object, practice, condition, belief, etc.