I am 41 years old
is a very different statement than
I am a vegan.
In the first case, there’s not a lot you can do about your “am”. It is an accurate description of a state of affairs over which you have no control.
In the second, it simply describes a choice. Anyone who wants to eat a certain way instantly becomes a vegan for as long as they make that choice.
The “am” that we think of as permanent identity might actually be a choice, repeated again and again.