When does it happen?

My mom still hasn't explained all those joke she was going to "tell me when I get older". Parents lie and they don't feel bad about it

when you realize your parents were just winging it

Well, I'm here to tell you now, each and every mother's son
You better learn it fast, you better learn it young
'Cause someday never comes
- First thing I thought of.
  
  It's haunting and timeless. One of their best.

I remember being told by a middle-aged co-worker back when I was 19 or 20 that I'm just young and that's why I have left wing views and when I'm her age, I'll be a Republican.
I'm now around her age and still not a Republican.
- I'm 35. The older I've got the more I've understood about the world and the more left wing I've become.
  The best part is it all started because as a religious child I got into red letter stuff, and took "love thy neighbour" to heart.
- Same here. Doubt I ever will considering, well, nazis.
  
  That and you're Canadian. 😜
  It was just such a weird thing to say too. Like she thought everyone her age was a Republican?

Now that I'm older I understand an awful lot of what they didn't explain and am still baffled by stuff they said I'd understand.

Just be patient, it'll come!

Young people understand a lot more than many adults give them credit for.

Exactly!

A lot of times the understanding is just that none of the adults actually knew what the fuck they were doing.

Here's the raw truth, as I understand it. I'm one of the people who has used this phrase. Typically I pull it out when I absolutely lack the ability to explain and verbalize something in a way that the intended audience can understand and accept. Yes, it's a failing on my part, but also, despite what everyone wants to believe, not everything can be distilled down to a simple easily understandable explanation without losing the message. You'll probably understand when you get older.
Realistically, it's not so much a guarantee that you'll understand the exact nature of what I'm saying when you're older. It's more that when you're older, you're probably going to be more willing to accept that I have my own perfectly valid reasons, even if I can't articulate them effectively, that the world is complicated, and sometimes it's those complicated and difficult to articulate threads that are actually the only things holding everything together. So, when I say you'll understand when you're older, I might not mean that in the most literal sense, it's very likely that I'm speaking more in a metaphorical way.
- My response would be that if you cannot explain your position, then you cannot defend it, and therefore you do not understand it yourself. This implies that you are simply feeling you way into your position using gut instincts, which are easily created and manipulated without a reasonably sound argument. An ad on TV, a op-ed piece only half heard, a slew of biased headlines, and more all contribute to these gut feelings without providing a rational base.
  In short, I reject your claim that complicated positions cannot be explained. Yes, many can't be easily explained, but you should still be able to explain and defend them.
  So when the position is challenged and you can't defend it because you have only these gut feelings at the core, you fall back on the belief that anyone would have the same feelings eventually. This is, of course, not true.

I understand a lot of shit now. It didn't make me feel better.

I hate that phrase so much.
It sole purpose is to belittle and dismiss the person you are talking to.
It tells the person that they are obviously unable to understand because of some unrelated trait. It's an ad-hominim that just shuts down the conversation.
It's only used by people that cannot actually defend their position, but rather than continue to discuss it, they would rather just shut out the other person.
It's them telling the other person "you are less than me which is why you are wrong, and you must simply accept that because you cannot possibly understand how I am right."

When you leave your physical body, you will have an understanding of everything. So, just wait.

I am so close to mix hydrochloric acid with potassium carbonate and drink it.