milestone in life
(important) milestone in (one's) life
An exceptionally momentous, significant, or impactful moment, situation, or event in one's life. There is no milestone in your life that will ever compare with the birth of your child. I knew even then that that conversation would prove to an important milestone in my life.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
milestone in someone's lifeand important milestone in someone's life
a very important event or point in one's life. (From the [former] stone markers at the side of a road showing the distance to or from a place.) Joan's wedding was a milestone in her mother's life. The birth of a child is a milestone in every parent's life.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.