The concept of growing up is as philosophical or maybe as arbitrary as time itself. Different countries have different laws that dictate when people are qualified as adults. Where there is a centralised government, it is likely that there is a law that specifies when you are "adult" enough to do certain things, such as consume alcohol, apply for credit and participate in sexual acts.
We joke a lot about adulting and how gruelling it can be but the concept of adulthood, like our perception of youth, can change, especially as we get older.
For one, the Covid-19 pandemic is likely to cause people to age. In my case, I think I might have aged at least three years in the past six months. Having said that, when a colleague of mine said that 2020 was a very long January (aka Januworry) I couldn't relate more.