Destinharbor saidI don't think people change all that much. Guys who are negative in attitude when young just get less careful about hiding it when older. The percentage of negative young guys here probably exceeds the percentage of negative older guys. Blaming a negative attitude on others (or experience--same thing) is just a cop out. An extension of who he is. So often you get what you give.
Knowing many from not just grade school but from the playground, fifty plus years later, my friends still comment how we are all pretty much just who we were growing up. Very fun to observe and engage.
To the OP's point, I've always been much more so a skeptic, much less so a cynic, though I certainly see some benefit to appropriately applied cynicism and some hindrance to being overly skeptical such as analysis paralysis which I have to guard against.
I've never known jadedness and I find it sad to see others missing the joy. Those are they who get bored. I'm pretty much thoroughly entertained by my own thoughts, so wonder if the jaded and bored are simply those who don't connect to themselves, expressing that as being disconnect to the world, thereby becoming bored, jaded, etc. And I think Destin's right that a lot of the kids who say now that they are bored are they who will be jaded.
What they are missing is curiosity, the expectation or allowance that even repetition might be at any moment interrupted with something new or something unseen before.
This came in very handy for me especially when going through my mom's Alzheimer's when she'd often repeat herself, sometimes immediately after the other. So I turned it into an exploratory game. Each time I'd approach the same thing from a different angle. I'd ask different questions. And sure as shit, that opened up new paths and more understanding.
A jaded person would have been bored to shit at best or frustrated into anger. I found it fascinating. In that, I knew love.