I hope you lot choose the same thing

[Violet]

The 'Age Lines' thing is entirely cultural. Not much mystery to it, really. I can understand questioning these lines, but they are set by the culture in which they exist. In the U.S. (most states) you must be 21 to drink alcohol, but you must only be 18 to fight and die in war (or do any other job, for that matter). You only have to be 17 to watch fighting and death on a movie screen, though. These lines do not make much sense to me, but I know that they can be changed if enough people are convinced they should be.

They make a great deal of sense if a: what the separator means is not really well understood, and is open to much interpretation (ie: 'what is an adult', 'what is an old person', 'what must a person be able to do before they can drink'), b: little significant change occurs by passing said line (ie: mostly conceptual changes, few actual changes to the rights/responsibilities/etc.), c: it is cheaper than being accurate, and close enough in many cases.

Otherwise... there really is no sound reason that I'm aware of for them.

As for identity, I totally agree with most of what you said. However, I think I might have a different definition of 'Identity' than you are using. I am me. That is my identity. Over time my physical mien may change, but I am still me. With experience and knowledge, my convictions and beliefs may change, yet... I am still me. My identity hasn't changed, but my 'self' has. I do know what you mean, though. I just wouldn't use the word identity.

There is more to identity than just the identity of the self

That really is the question though... how much change is necessary before you really aren't "you" any more? And what used to be you is no longer you... how can that really be considered to be you when you are demonstrably much different from then?