settle down

[angliholic]

A friend asked me why I kept a low-key recently. And I told her that I needed to settle down/calm myself down and live a more serious and responsible life.


By the part in bold, I mean I want to remain quiet and silent so that I can think more deeply about life. Correct me if I say it wrong. Thanks.

[Anglika]

A friend asked me why I kept a low-key [had been so low-key] recently. And I told her that I needed to settle down/calm myself down and live a more serious and responsible life.

"Settle down" would be more usual.

[angliholic]

Thanks, Anglika.
Based on your advice, I'll rephrase my sentence:
A friend asked me why I had been so low-key recently. And I told her that I needed to settle down and live a more serious and responsible life.