Adulthood — the period when a person is considered an adult, typically after adolescence and involving independence and social responsibilities.
成人期には自分の健康管理を自分で行う必要がある。
In adulthood you need to manage your own health.
青年期から成人期への移行は人それぞれペースが違う。
The transition from adolescence to adulthood occurs at a different pace for everyone.