When you aren't in a place you think you should be, given your own values, and taking into account your own problems, the things outside your control that have affected you, and the options available to you.
This implicitly relies on actually identifying your values, spending a lot of time thinking about your life, understanding how factors outside your control have shaped things, and where you realistically think you should be. If you aren't there, you then very carefully and kindly consider what it is that's stopping you, what you can do to get there, and reasonably do your best to move forwards (taking into account your issues).
If you want someone to say "you should have lost your virginity by age blah blah" or "you should have your own house by blah blah" zero chance I would do this, because I have no clue what anyone else's life has been like.
I don't even know if someone else has the value of "must achieve milestones", so how could I tell them they must have done something. If someone has the value of purposefully not achieving socially acceptable goals, they can be way ahead, and that's fine. Other peoples values and goals not my concern.