I don't understand the idea that just slapping down any code that can limp through QA is "faster" than doing things in a well-organized way that follows best practice. For one thing, it's not actually faster to write (particularly if you do have decades of experience rather than being a relative newbie who just happens to be older than those around him). And then, as you rightly point out, that code that was just randomly slapped into place is impossible to build upon and has to be rewritten or you spend lots of extra time in perpetuity working around its flaws. Best practices exist precisely to facilitate faster development than just slapping down code.

By the same token, frameworks exist because cowboy coders just don't arrive at well-architected solutions on their own. They just don't. And so frameworks exist to give everybody, not just people who happen to know how to architect things, at least some kind of common approach that at least everyone is doing things roughly the same way. Even if you could come up with something WAAAY better than the best engineers at Google or Facebook, you couldn't hire people off the street who were already familiar with it, and you'd have to maintain all the underlying code and the tests for it, which would distract from your actual business purpose.

Ageism from young to old is really illogical if you think about it. It's like they don't plan to be doing the same job anymore when they hit 40 or 50, or they think they'll somehow get stupid between now and then. Because, face it, we were all their age once. But that's the kind of perspective that comes with age and experience.

Finally, many people, not just young people, take it as an implicit criticism when you decide to do things radically different to how they are doing it (especially if you succeed). This is just human nature, and while it doesn't feel great, with experience you learn it just goes with the territory.