You are right that we all make assumptions about others based on our own experience. And we also base our assumptions on what we've learned from our own families, and from the culture at large.
No matter what we believe, we are all right to the degree those stereotypical assumptions are based on some truth. There are hard-working ants, and lazy, fun-loving grasshoppers.
The problem is, the poor are mostly working and struggling, and are only a hair's breadth away from financial disaster. A crisis that would be a difficulty in an upper-middle-class familly can have dire consequences for the working poor. A serious illness or parent or child can get a poor mother fired. An accident, an unplanned pregnancy, a theft of workman's tools – I've watched all of these, which would hardly phase a rich family, result in loss of critical income, home, or car.
I knew a mom whose two children were placed in foster homes because she lost her job through no fault of her own, lost her rented apartment, was unable to get a job because her car had no address, she had no telephone (before cell phones were available). Friends gave her and her kids a place to crash, eat and shower when they could, but her friends were low-income, too, and could only help so much. So she lost her beloved babies. It was a heartbreaking situation to watch, and to have no power to change.
Finally, a taxpayer-supported social program helped this mom retrain for a better-paying position, and an agency found her a job. It still took a couple of years for her to "earn" her children back, even though that would have cost "us" less than the foster homes they were in. She was one of the hardest-working, eager and hopeful people I've ever known. Not the brightest, but then, how many of us can realistically be "The Brightest"?
The rant by the 21-year-old posted earlier had no room in it for people like this, who I'm pretty sure, based on my own experiences as a low-income worker, are not the exception.
So I would say that inexperience does not necessarily link to age. Certainly the quality of the response does link to inexperience, however, and the age of that ranter was placed in the spotlight in that earlier post.