Noun にして初めて (Noun nishite hajimete)

Otona ni shite hajimete, oya no kurou ga wakatta.

Only when I became an adult did I understand my parents' struggles for the first time.

Kare wa yonjuu-sai ni shite hajimete, kaigai ryokou o keiken shita.

Only when he turned 40 did he travel abroad for the first time.

Kanojo wa oya ni shite hajimete, kosodate no taihensa o rikai shita.

It was only after she became a parent that she realized how challenging raising a child can be.

Shachou ni shite hajimete, kaisha zentai no juuseki o tsuukan shita.

Only when he became president did he feel the full weight of responsibility for the entire company.