I think that evolution isn’t always as linear as that, but still, it seems that most souls do go through this kind of process.
On Earth, then, a lot of souls have started out millenia ago as cavepeople and have evolved to where they are now.
The indigo who doesn’t look like an indigo will, deep down, have that wisdom, that depth, that power you expect from a normal indigo. Someone who looks like an indigo but isn’t will seem deep but when you look closer there won’t be so much substance to them.
It’ll be a false depth — or maybe an authentic one, but just not so much of it. The standard depiction of spiritual evolution shows a soul starting out from a very basic, caveperson-like consciousness, and going through the horrible birthing pain centuries of confusion and war, eventually evolving into a modern human, eventually becoming enlightened or a saint.
Or, if the indigo in your life happens to be someone other than you, the goal is to understand her or him as best you can and again, be better equipped to accept them as they are. The , then, is that indigos are, in general, old souls or at least souls with great spiritual depth.