today is the first day of the rest of (someone's) life

Translations
сегодня - первый день остатка (чьей-то) жизни
Remember, today is the first day of the rest of your life.
Помни, сегодня - первый день остатка твоей жизни.
Definitions
This phrase suggests that each new day presents an opportunity for a fresh start or a new beginning, emphasizing the idea that one can change their life or make new choices starting from today.