Fetching details from the dictionary...

person of virtue; great person; magnanimous person
giant
adult
exalted person
あの方はまさに大人だ。
That person is truly a great man.
大人の風格を持つ人は尊敬される。
A person with the bearing of a great man is respected.
大人と呼ばれるにふさわしい人になりたいです。
I want to become a person worthy of being called a great man.