I agree that every kid will and should go about making their own mistakes. I don't see anything wrong with warning kids though. Obviously they are not always going to listen, but on some accounts they will. Some of the things I did landed me in so much trouble, I'd wished someone had tested the waters for me and let me know I might regret it.
To say that any kid who listens to what the adults in his life tell him is either really stupid or scared is a pretty dumb statement. I didn't always listen to my parents, but on many occasions I did, not because I was scared or stupid, but because I had a great deal of respect for my parents and didn't want to disappoint them.
It would be irresponsible parenting to not warn your kids about some of the hardships you have gone through on account of stupid things you have done. By sharing with them your own experiences you cannot expect them to learn 100% from your experiences, but the hope is that they will take them into account and possibly save themselves some trouble.
I wouldn't say YIYF is immature for not wanting to conform to standards and dress the way most other adults around him do. But I also wouldn't say his friends are scared weak old men. Seriously, why does this make them scared and weak? Come on!
My grandfather felt comic books and video games were foolish wastes of time (and I actually agree with him 100%, though they were things I felt worthy of wasting my time on as a kid). The idea of calling my grandfather scared and weak for his feelings on these things would be absurd! The man survived WW2, was tough as nails, could work from sun up until sun down without taking a break, and was afraid of nothing as far as I could ever tell. These were things he didn't understand, they were things that had no use or merit in his eyes. Wasting hours staring at the TV making a little plumber run around and squash turtles just didn't make any sense to him. Reading stories in colorful books about people who wear tights and have magical powers didn't make any sense to him. Zipping around on skateboards, wearing baggy clothes and refusing to get a hair cut didn't make any sense to him.
So what? It is a generation gap, it is a differing of values, a difference in culture. It is normal and to be expected. When he was that age, he was getting up at the break of dawn everyday and helping to run his families farm. Of course he is going to look at me sleeping in until noon every time I got the chance, waking up and sitting in front of the Nintendo for a couple of hours before donning my backwards hat and baggy clothes and running off with my other baggy clothed friends as a complete waste of time and as being up to no good. Ha, half the time I was up to no good! So his feelings seem to have been pretty air tight.
And in all fairness you do have youths who go around and vandalize, thieve, and carry out other thuggish acts. When I was a youth I was looked upon with distrust by older people, but why not? When there are stories in the news about kids who dress and act like me doing these sorts of things. It bothered me a bit when I was a kid, but I always felt it was perfectly reasonable for them to feel this way.
I feel it is rather closed minded to hold these things against our older generations. The best you can have done was to show them there is nothing to worry about, and to keep your mind open when a younger, stranger generation than yourself comes along.