As others said, when you're financially able to or when you or your parents recognize it's time to leave.

Society likes to label people who live with their parents as losers, but there are plenty of good reasons to continue to live with them where the living arrangements are mutually beneficial to both the parents and offspring.

The bigger thing is to not be dependent on them. Even better if they can rely on you.

This obviously doesn't apply to people who are dealing with medical or mental impairments where they rely on their parents because they can't take care of themselves. Even then though, most people don't want to be a permanent caregivers and eventually you'll have to figure out other arrangements, especially when your parents reach an age where they need help themselves.